गणवतता नीति
रलो ो म यातरी और माल यािायाि की बढ़िी मााग को परा करन क तलए
गणवतता परबोध परणाली म अनसोधान तिज़ाइनो ो और मानकोो म उतकषटिा िथा
सिि सधारो ो क माधयम स साोतवतधक और तनयामक अपकषाओो को परा करि
हए सरतकषि आधतनक और तकफ़ायिी रल परौदयोतगकी का तवकास करना
QUALITY POLICY
To develop safe modern and cost effective Railway technology
complying with Statutory and Regulatory requirements through
excellence in Research Designs amp Standards and Continual
improvements in Quality Management System to cater to
growing demand of passenger and freight traffic on the
Railways
COPYRIGHT copy 2017 by CAMTECH Gwalior and RDSO Lucknow
All rights reserved No part of this publication may be reproduced by any means without the prior written
permission
FOREWORD
It is very heartening to know that a Handbook on Construction of
Earthquake Resistant Buildings is being brought out by CAMTECH Directorate
Gwalior under the aegis of RDSO The complex theory and practical issues
related to Earthquake magnitude its measurement earthquake resistant design
preferred building layout and design based on Earthquake spectrum analysis has been
presented in a lucid and informative manner for adoption in the field by Civil
Engineers Solvedmiddot examples have also been included illustrating calculation of design
forces in structural member for multi-storied building Provisions
contained in Seismic Code IS 1893 amp others have been brought out related to
building layout seismic forces calculation and reinforcement detailing
Details of retro-fitment for buildings have been also included which can
adopted by serving Engineers to make buildings Earthquake Resistant in an
effective and economical manner
I congratulate ADG and EDWorks of RDSO for editing amp Civil Engineers
of CAMTECH for compilation of very informative Handbook
New Delhi 20
th July 2017
vkfnR dqekj feRry AK MITTAL
F o r e w o r d
It is indeed very heartening to know that CAMTECH under the direction from RDSO has brought out a Handbook on ldquoConstruction of Earthquake Resistant Buildingsrdquo
It is also worth mentioning that on IR there were no comprehensive Guidelines or instructions regarding construction of Earthquake Resistant Buildings This handbook shall bridge the gap amp provide technical information on Earthquake phenomenon assessment of magnitude of earthquake general principles for earthquake resistance in Building-layout dynamic response of Buildings
Codal based procedure for determining lateral earthquake forces with special
reference to lsquoDuctility amp Capacity Design Conceptsrsquo has been brought out Solved examples illustrate calculation of design forces for structural members of multi-storied building Provisions contained in Seismic Code IS 1893 amp others have been brought out related to buildings which shall help structural designers and project engineers Chapter on Seismic Evaluation and Retrofitting gives in-sight to serving Engineers in the field to assess building for earthquake resistance and action required thereof in economical manner Thanks are due to Dr SK Thakkar Professor (Retd) IITRoorkee for technical review of this Handbook I congratulate Works amp Bridge Dte of RDSO for editing and Sh DK Gupta Jt Director Civil of CAMTECH involved in compilation of this Handbook for their praise worthy efforts
(J S Sondhi) Addl Director General
RDSO Dt 20072017
पराककथन
दनिया क कई निससो म िाल िी म आए भको पसो ि इमारतसो और जीवि कस काफी िकसाि पहोचाया ि भको प की दनि स दखा जाए तस सबस खतरिाक भवि निमााण
unreinforced ईोट या concrete बलॉक का िसता ि चार मोनजलसो तक क अनिकाोश घरसो कस परबनलत को करीट सलब क साथ burnt clay ईोट नचिाई स निनमात नकया जा रिा ि इसी तरि कई िए चार या पाोच मोनजला घर जस नक छसट और बड शिरसो म परबनलत को करीट फरम स बिाए गए ि म एक उनचत फरम परणाली की कमी रिती ि
िाल िी म आए भको पसो क कारण भारत म इमारतसो और घरसो कस कस सरनित रखा जाय इस पर परमखता स चचाा हई ि भको पीय दशसो म इोजीनियसा कस यि मितवपणा नजममदारी सनिनित करिा ि नक िए निमााण भको प परनतरसिी िसो और यि भी नक उनह मौजदा कमजसर सोरचिाओो दवारा उतपनन समसया का समािाि भी निकालिा ि
यि आशा की जाती ि नक कमटक दवारा तयार पसतिका नसनवल सोरचिाओो क निमााण एवो रखरखाव की गनतनवनियसो म लग भारतीय रलव क इोजीनियररोग कनमायसो क नलए काफी मददगार िसगी
कमटक गवातलयर (ए आर िप) 23 मई 2017 काययकारी तनदशक
FOREWORD
The recent earthquakes occurred in many parts of world has caused considerable damage
to the buildings and lives The most dangerous building construction from an
earthquake point of view is unreinforced brick or concrete block Most houses of upto
four storeys are built of burnt clay brick masonry with reinforced concrete slabs
Similarly many new four or five storey reinforced concrete frame building being
constructed in small and large towns lack a proper frame system
With the recent earthquakes the discussion on how safe buildings and houses are in
India has gained prominence Engineers in seismic countries have the important
responsibility to ensure that the new construction is earthquake resistant and also they
must solve the problem posed by existing weak structures
It is expected that the handbook prepared by CAMTECH will be quite helpful to the
engineering personnel of Indian Railways engaged in construction and maintenance
activities of civil structures
CAMTECHGwalior (AR Tupe)
23 May 2017 Executive Director
भतमका
भारतीय रलव एक बड़ा सगठन ह जिसक पास ससववल इिीननयररग सरचनाओ एव भवनो की ववशाल सपदा मौिद ह भकप की ववनाशकारी परकनत को धयान म रखत हए यह आवशयक ह कक लगभग सभी भवनो चाह व आवासीय ससथागत शकषणिक इतयादद क हो उनकी योिना डििाइन ननमााि तथा रखरखाव भकप परनतरोधी तरीको को अपनाकर ककया िाना चादहए जिसस कक भकप क कारि मानव िीवन व सपवि क नकसान को नयनतम ककया िा सक
ldquoभकप परतिरोधी भवनो क तनरमाणrdquo पर यह हसतपजसतका एक िगह पर पयाापत सामगरी परदान करन का एक परयास ह ताकक वयजतत भवनो क भकप परनतरोधी ननमााि क सलए मलभत ससदधातो को ववकससत कर सही तथा वयवहाररक कायाववधध को अमल म ला सक
इस हसतपजसतका की सामगरी को गयारह अधयायो म ववभाजित ककया गया ह अधयमय-1 पररचय तथा अधयमय-2 भकप इिीननयररग म परयतत शबदावली पररभावित करता ह अधयमय-3 भकप व भकपी खतरो क बार म बननयादी जञान को सकषप म वणिात करता ह अधयमय- 4 भकप पररमाि तथा तीवरता क माप क साथ भारत क भकपीय ज़ोन मानधचतर भकप की ननगरानी क सलए एिससयो क बार म िानकारी परदान करता ह अधयमय-5 व 6 भवन लआउट म भकप परनतरोध क सधार क सलए वयापक ससदधात को बताता ह अधयमय-7 भवन की गनतशील परनतकिया को दशााता ह अधयमय-8 और 9 म कोि पर आधाररत पाशवा बल ननधाारि का तरीका तथा बहमजिला भवन की ldquoितटाइल डिटसलग तथा कपससटी डििाइनrdquo को धयान म रखत हए डििाइन का उदाहरि परसतत ककया गया ह अधयमय-10 म कम शजतत की धचनाई दवारा सरचनाओ क ननमााि को भकप परनतरोधी ससदधातो को धयान म रख वणिात ककया गया ह अधयमय -11 म मौिदा भवनो की भकप परनतरोधी आवशयकताओ को परा करन क सलए भवनो क मौिदा भकपरोधी मलयाकन और पनः सयोिन पर परकाश िाला गया ह
यह हसतपजसतका मखयतः भारतीय रल क फीलि तथा डििाइन कायाालय म कायारत िईएसएसई सतर क सलए ह इस हसतपजसतका को भारतीय रल क ससववल इिीननयसा तथा अनय ववभागो क इिीननयसा दवारा एक सदभा पजसतका क रप म भी इसतमाल ककया िा सकता ह
म शरी एस क ठतकर परोफसर (ररटायिा) आई आई टी रड़की को उनक दवारा ददय गए मागादशान तथा सझावो क सलए अतयनत आभारी ह तथा शरी क सी शातय एसएसईससववल को इस हसतपजसतका क सकलन म उनक समवपात सहयोग क सलए धनयवाद दता ह
यदयवप इस हसतपजसतका को तयार करन म हर तरह की सावधानी बरती गई ह कफर भी कोई तरदट या चक हो तो कपया IRCAMTECHGwalior की िानकारी म लायी िा सकती ह
भारतीय रल क सभी अधधकाररयो और इकाइयो दवारा पसतक की सामगरी म ववसतार तथा सधार क सलए ददय िान वाल सझावो का सवागत ह
कमटक गवातलयर (िी क गपता) 23 मई 2017 सोयकत तनदशकतसतवल
PREFACE
Indian Railways is a big organisation having large assets of Civil Engineering Structures
and Buildings Keeping in mind the destructive nature of Earthquake it is essential that
almost all buildings whether residential institutional educational assembly etc should
be planned designed constructed as well as maintained by adopting Earthquake
Resistant features so that loss due to earthquake to human lives and properties can be
minimised
This handbook on ldquoConstruction of Earthquake Resistant Buildingsrdquo is an attempt to
provide enough material at one place for individual to develop the basic concept for
correctly interpreting and using practices for earthquake resistant construction of
Buildings
Content of this handbook is divided into Eleven Chapters Chapter-1 is Introduction
and Chapter-2 defines Terminology frequently used in Earthquake Engineering
Chapter-3 describes in brief Basic knowledge about Earthquake amp Seismic Hazards
Chapter-4 deals with Measurement of Earthquake magnitude amp intensity with
information about Seismic Zoning Map of India and Agencies for Earthquake
monitoring Chapter-5 amp 6 elaborates General Principle for improving Earthquake
resistance in building layouts Chapter-7 features Dynamic Response of Building In
Chapter-8 amp 9 Codal based procedure for determining lateral loads and Design of
multi-storeyed building with solved example considering Ductile Detailing and Capacity
Design Concept is covered Chapter-10 describes Construction of Low strength
Masonry Structure considering earthquake resistant aspect Chapter-11 enlighten
ldquoSeismic Evaluation amp Retrofittingrdquo for structural upgrading of existing buildings to
meet the seismic requirements
This handbook is primarily written for JESSE level over Indian Railways working in
Field and Design office This handbook can also be used as a reference book by Civil
Engineers and Engineers of other departments of Indian Railways
I sincerely acknowledge the valuable guidance amp suggestion by Shri SK Thakkar
Professor (Retd) IIT Roorkee and also thankful to Shri KC Shakya SSECivil for his
dedicated cooperation in compilation of this handbook
Though every care has been taken in preparing this handbook any error or omission
may please be brought out to the notice of IRCAMTECHGwalior
Suggestion for addition and improvement in the contents from all officers amp units of
Indian Railways are most welcome
CAMTECHGwalior (DK Gupta)
23 May 2017 Joint DirectorCivil
तवषय-सची CONTENT
अधयाय CHAPTER
तववरण DESCRIPTION
पषठ
सोPAGE
NO
पराककथन FOREWORD FROM MEMBER ENGINEERING RLY BOARD पराककथन FOREWORD FROM ADG RDSO पराककथन FOREWORD FROM ED CAMTECH भतमका PREFACE
तवषय-सची CONTENT
सोशोधन पतचययाो CORRECTION SLIPS
1 पररचय Introduction 01
2 भको प इोजीतनयररोग क तलए शबदावली Terminology for Earthquake
Engineering 02-05
3 भको प क बार म About Earthquake 06-16
31 भको प Earthquake 06
32 नकि कारणसो स िसता ि भको प What causes Earthquake 06
33 नववतानिक गनतनवनि Tectonic Activity 06
34 नववतानिक पलट का नसदाोत Theory of Plate Tectonics 07
35 लचीला ररबाउोड नसदाोत Elastic Rebound Theory 11
36 भको प और दसष क परकार Types of Earthquakes and Faults 11
37 जमीि कस निलती ि How the Ground shakes 12
38 भको प या भको पी खतरसो का परभाव Effects of Earthquake or Seismic
Hazards 13
4 भको पी जोन और भको प का मापन Seismic Zone and Measurement
of Earthquake 17-28
41 भको पी जसि Seismic Zone 17
42 भको प का मापि Measurement of Earthquake 19
43 भको प पररमाण सकल क परकार Types of Earthquake Magnitude
Scales 20
44 भको प तीवरता Earthquake Intensity 22
45 भको प निगरािी और सवाओो क नलए एजनसयसो Agencies for Earthquake
Monitoring and Services 28
5 भवन म भको प परतिरोध म सधार क तलए सामानय तसदाोि General
Principle for improving Earthquake Resistance in Building 29-33
51 िलकापि Lightness 29
52 निमााण की निरोतरता Continuity of Construction 29
53 परसजसतटोग एवो ससपडड पाटटास Projecting and Suspended Parts 29
54 भवि की आकनत Shape of Building 29
55 सनविा जिक नबसतडोग लआउट Preferred Building Layouts 30
56 नवनभनन नदशाओो म शसति Strength in Various Directions 30
57 िी ोव Foundations 30
58 छत एवो मोनजल Roofs and Floors 30
59 सीनियाो Staircases 31
510 बॉकस परकार निमााण Box Type Construction 33
511 अनि सरिा Fire Safety 33
6
भको प क दौरान आर सी भवनो ो क परदशयन पर सटरकचरल अतनयतमििाओो
का परभाव Effect of Structural Irregularities on Performance of
RC Buildings during Earthquakes
34-38
61 सटर कचरल अनियनमतताओो का परभाव Effect of Structural Irregularities 34
62 िनतज अनियनमतताएो Horizontal Irregularities 34
63 ऊरधाािर अनियनमतताएो Vertical Irregularities 36
64
भवि नवनयास अनियनमतताएो ndash समसयाए ववशलिि एव ननदान क उपाय Building Irregularities ndash Problems Analysis and Remedial
Measures 37
7 भवन की िायनातमक तवशषिाएा Dynamic Characteristics of
Building 39-47
71 डायिानमक नवशषताए Dynamic Characteristics 39
72 पराकनतक अवनि Natural Period 39
73 पराकनतक आवनि Natural Frequency 39
74 पराकनतक अवनि कस परभानवत करि वाल कारक Factors influencing
Natural Period 40
75 Mode आकनत Mode Shape 42
76 Mode आकनतयसो कस परभानवत करि वाल कारक Factors influencing
Mode Shapes 44
77 सोरचिा की परनतनकरया Response of Structure 46
78 नडजाइि सपटर म Design Spectrum 46
8 तिजाइन पारशय बलो ो क तनधायरण क तलए कोि आधाररि िरीका Code
Based Procedure for Determination of Design Lateral Loads 48-59
81 भको पी नडजाइि की नफलससफ़ी Philosophy of Seismic Design 48
82 भको पी नवशलषण क नलए तरीक Methods for Seismic Analysis 48
83 डायिानमक नवशलषण Dynamic Analysis 49
84 पारशा बल परनकरया Lateral Force Procedure 49
85 को पि की मौनलक पराकनतक अवनि Fundamental Natural Period of
Vibration 52
86 नडजाइि पारशा बल Design Lateral Force 53
87 नडजाइि बल का नवतरण Distribution of Design Force 53
88 नडजाइि उदािरण Design Example ndash To determine Base Shear and
its distribution along Height of Building 54
9 ढााचागि सोरचना का तनमायण Construction of Framed Structure 60-90
91
गरतवाकषाण लसनडोग और भको प लसनडोग म आर सी नबसतडोग का वयविार Behaviour of RC Building in Gravity Loading and Earthquake
Loading 60
92 परबनलत को करीट इमारतसो पर िनतज भको प का परभाव Effect of Horizontal
Earthquake Force on RC Buildings 61
93 िमता नडजाइि सोकलपिा Capacity Design Concept 61
94 लचीलापि और ऊजाा का अपवयय Ductility and Energy Dissipation 62
95 lsquoमजबतिोभ ndash कमजसर बीमrsquo फलससफ़ी lsquoStrong Column ndash Weak
Beamrsquo Philosophy 62
96 कठसर डायाफराम नकरया Rigid Diaphragm Action 63
97
सॉफट सटसरी नबसतडोग क साथ ndash ओपि गराउोड सटसरी नबसतडोग जस नक भको प क
समय कमजसर िसती ि Building with Soft storey ndash Open Ground
Storey Building that is vulnerable in Earthquake 63
98 भको प क दौराि लघ कॉलम वाली इमारतसो का वयविार Behavior of
Buildings with Short Columns during Earthquakes 65
99 भको प परनतरसिी इमारतसो की लचीलापि आवशयकताए Ductility
requirements of Earthquake Resistant Buildings 66
910
बीम नजनह आर सी इमारतसो म भको प बलसो का नवरसि करि क नलए डाला जाता
ि Beams that are required to resist Earthquake Forces in RC
Buildings 66
911 फलकसचरल ममबसा क नलए सामानय आवशयकताए General Requirements
for Flexural Members 68
912
कॉलम नजनह आर सी इमारतसो म भको प बलसो का नवरसि करि क नलए डाला
जाता ि Columns that are required to resist Earthquake Forces in
RC Buildings 69
913 एकसीयल लसडड मबसा क नलए सामानय आवशयकताए General
Requirements for Axial Loaded Members 71
914 बीम-कॉलम जसड जस आर सी भविसो म भको प बलसो का नवरसि करत ि Beam-
Column Joints that resist Earthquakes Forces in RC Buildings 72
915 नवशष सीनमत सदढीकरण Special Confining Reinforcement 74
916
नवशषतः भको पीय ितर म कतरिी दीवारसो वाली इमारतसो का निमााण Construction of Buildings with Shear Walls preferably in Seismic
Regions 75
917 इमपरवड नडजाइि रणिीनतयाो Improved design strategies 76
918 नडजाइि उदािरण Design Example ndash Beam Design of RC Frame
with Ductile Detailing 78
10 अलप सामरथय तचनाई सोरचनाओो क तनमायण Construction of Low
Strength Masonry Structures 91-106
101 भको प क दौराि ईोट नचिाई की दीवारसो का वयविार Behaviour of
Brick Masonry Walls during Earthquakes 91
102 नचिाई वाली इमारतसो म बॉकस एकशि कस सनिनित कर How to ensure
Box Action in Masonry Buildings 92
103 िनतज बड की भनमका Role of Horizontal Bands 93
104 अिसलोब सदढीकरण Vertical Reinforcement 95
105 दीवारसो म सराखसो का सोरिण Protection of Openings in Walls 96
106
भको प परनतरसिी ईोट नचिाई भवि क निमााण ित सामानय नसदाोत General
Principles for Construction of Earthquake Resistant Brick
Masonry Building
97
107 ओपनिोग का परभाव Influence of Openings 100
108 िारक दीवारसो म ओपनिोग परदाि करि की सामानय आवशयकताए General Requirements of Providing Openings in Bearing Walls
100
109 भको पी सदिीकरण वयवसथा Seismic Strengthening Arrangements 101
1010 भको प क दौराि सटसि नचिाई की दीवारसो का वयविार Behaviour of Stone
Masonry Walls during Earthquakes 104
1011
भकप परनतरोधी सटोन धचनाई क ननमााि हत सामानय ससदधात General
Principles for Construction of Earthquake Resistant Stone
Masonry Building
104
11 भकपीय रलयमकन और रटरोफिट ग Seismic Evaluation and
Retrofitting 107-142
111 भकपीय मलयाकन Seismic Evaluation 107
112 भवनो की रटरोकिदटग Retrofitting of Building 116
113
आरसी भवनो क घटको म सामानय भकपी कषनतया और उनक उपचार Common seismic damage in components of RC
Buildings and their remedies 133
114 धचनाई सरचनाओ की रटरोकिदटग Retrofitting of Masonry
Structures 141
Annex ndash I भारिीय भको पी सोतििाएा Indian Seismic Codes 143-145
Annex ndash II Checklist Multiple Choice Questions for Points to be kept in
mind during Construction of Earthquake Resistant Building 146-151
सोदभयगरोथ सची BIBLIOGRAPHY 152
तटपपणी NOTES 153-154
हमारा उददशय एव डिसकलरर OUR OBJECTIVE AND DISCLAIMER
सोशसिि पनचायसो का परकाशि
ISSUE OF CORRECTION SLIPS
इस ििपसतिका क नलए भनवषय म परकानशत िसि वाली सोशसिि पनचायसो कस निमनािसार सोखाोनकत
नकया जाएगा
The correction slips to be issued in future for this handbook will be numbered as
follows
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CAMTECH2017CERB10CS XX date_________________________
जिा xx सोबसतित सोशसिि पची की करम सोखा ि (01 स परारमभ िसकर आग की ओर)
Where ldquoXXrdquo is the serial number of the concerned correction slip (starting
from 01 onwards)
परकातशि सोशोधन पतचययाा W a
CORRECTION SLIPS ISSUED
करसो Sr No
परकाशन
तदनाोक Date of
issue
सोशोतधि पषठ सोखया िथा मद सोखया Page no and Item No modified
तटपपणी Remarks
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अधयाय Chapter ndash 1
पररचय Introduction
To avoid a great earthquake disaster with its severe consequences special consideration must be
given Engineers in seismic countries have the important responsibility to ensure that the new
construction is earthquake resistant and also they must solve the problem posed by existing weak
structures
Most of the loss of life in past earthquakes has occurred due to the collapse of buildings
constructed with traditional materials like stone brick adobe (kachcha house) and wood which
were not particularly engineered to be earthquake resistant In view of the continued use of such
buildings it is essential to introduce earthquake resistance features in their construction
The problem of earthquake engineering can be divided into two parts first to design new
structures to perform satisfactorily during an earthquake and second to retrofit existing structures
so as to reduce the loss of life during an earthquake Every city in the world has a significant
proportion of existing unsafe buildings which will produce a disaster in the event of a strong
ground shaking Engineers have the responsibility to develop appropriate methods of retrofit
which can be applied when the occasion arises
The design of new building to withstand ground shaking is prime responsibility of engineers and
much progress has been made during the past 40 years Many advances have been made such as
the design of ductile reinforced concrete members Methods of base isolation and methods of
increasing the damping in structures are now being utilized for important buildings both new and
existing Improvements in seismic design are continuing to be made such as permitting safe
inelastic deformations in the event of very strong ground shaking
A problem that the engineer must share with the seismologistgeologist is that of prediction of
future occurrence of earthquake which is not possible in current scenario
Earthquake resistant construction requires seismic considerations at all stages from architectural
planning to structural design to actual constructions and quality control
Problems pertaining to Earthquake engineering in a seismic country cannot be solved in a short
time so engineers must be prepared to continue working to improve public safety during
earthquake In time they must control the performance of structures so that effect of earthquake
does not create panic in society and its after effects are easily restorable
To ensure seismic resistant construction earthquake engineering knowledge needs to spread to a
broad spectrum of professional engineers within the country rather than confining it to a few
organizations or individuals as if it were a super-speciality
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अधयाय Chapter ndash 2
भको प इोजीतनयररोग क तलए शबदावली Terminology for Earthquake Engineering
21 फोकस या िाइपोसटर Focus or Hypocenter
In an earthquake the waves emanate from a finite area
of rocks However the point from which the waves
first emanate or where the fault movement starts is
called the earthquake focus or hypocenter
22 इपीसटर Epicentre
The point on the ground surface just above the focus is called the epicentre
23 सििी फोकस भको प Shallow Focus Earthquake
Shallow focus earthquake occurs where the focus is less than 70 km deep from ground surface
24 इोटरमीतिएट फोकस भको प Intermediate Focus Earthquake
Intermediate focus earthquake occurs where the focus is between 70 km to 300 km deep
25 गिरा फोकस भको प Deep Focus Earthquake
Deep focus earthquake occurs where the depth of focus is more than 300 km
26 इपीसटर दरी Epicentre Distance
Distance between epicentre and recording station in km or in degrees is called epicentre distance
27 पवय क झटक Foreshocks
Fore shocks are smaller earthquakes that precede the main earthquake
28 बाद क झटक Aftershocks
Aftershocks are smaller earthquakes that follow the main earthquake
29 पररमाण Magnitude
The magnitude of earthquake is a number which is a measure of energy released in an
earthquake It is defined as logarithm to the base 10 of the maximum trace amplitude expressed
in microns which the standard short-period torsion seismometer (with a period of 08s
Fig 21Basic terminology
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magnification 2800 and damping nearly critical) would register due to the earthquake at an
epicentral distance of 100 km
210 िीवरिा Intensity
The intensity of an earthquake at a place is a measure of the strength of shaking during the
earthquake and is indicated by a number according to the modified Mercalli Scale or MSK
Scale of seismic intensities
211 पररमाण और िीवरिा क बीच बतनयादी फकय Basic difference between Magnitude and
Intensity
Magnitude of an earthquake is a measure of its size
whereas intensity is an indicator of the severity of
shaking generated at a given location Clearly the
severity of shaking is much higher near the
epicenter than farther away
This can be elaborated by considering the analogy
of an electric bulb Here the size of the bulb (100-
Watt) is like the magnitude of an earthquake (M)
and the illumination (measured in lumens) at a
location like the intensity of shaking at that location
(Fig 22)
212 दरवण Liquefaction
Liquefaction is a state in saturated cohesion-less soil wherein the effective shear strength is
reduced to negligible value for all engineering purpose due to pore pressure caused by vibrations
during an earthquake when they approach the total confining pressure In this condition the soil
tends to behave like a fluid mass
213 तववियतनक लकषण Tectonic Feature
The nature of geological formation of the bedrock in the earthrsquos crust revealing regions
characterized by structural features such as dislocation distortion faults folding thrusts
volcanoes with their age of formation which are directly involved in the earth movement or
quake resulting in the above consequences
214 भको पी दरवयमान Seismic Mass
It is the seismic weight divided by acceleration due to gravity
215 भको पी भार Seismic Weight
It is the total dead load plus appropriate amounts of specified imposed load
Fig 22 Reducing illumination with distance
from an electric bulb
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216 आधार Base
It is the level at which inertia forces generated in the structure are transferred to the foundation
which then transfers these forces to the ground
217 दरवयमान का क दर Centre of Mass
The point through which the resultant of the masses of a system acts is called Centre of Mass
This point corresponds to the centre of gravity of masses of system
218 कठोरिा का क दर Centre of Stiffness
The point through which the resultant of the restoring forces of a system acts is called Centre of
stiffness
219 बॉकस परणाली Box System
Box is a bearing wall structure without a space frame where the horizontal forces are resisted by
the walls acting as shear walls
220 पटटा Band
A reinforced concrete reinforced brick or wooden runner provided horizontally in the walls to tie
them together and to impart horizontal bending strength in them
221 लचीलापन Ductility
Ductility of a structure or its members is the capacity to undergo large inelastic deformations
without significant loss of strength or stiffness
222 किरनी दीवार Shear Wall
Shear wall is a wall that is primarily designed to resist lateral forces in its own plane
223 िनय का बयौरा Ductile Detailing
Ductile Detailing is the preferred choice of location and amount of reinforcement in reinforced
concrete structures to provide adequate ductility In steel structures it is the design of members
and their connections to make them adequate ductile
224 लचीला भको पी तवरण गणाोक Elastic Seismic Acceleration Co-Efficient A
This is the horizontal acceleration value as a fraction of acceleration due to gravity versus
natural period of vibration T that shall be used in design of structures
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225 पराकतिक अवतध Natural Period T
Natural period of a structure is its time period of undamped vibration
a) Fundamental Natural Period Tl It is the highest modal time period of vibration along the
considered direction of earthquake motion
b) Modal Natural Period Tk Modal natural period of mode k is the time period of vibration in
mode k
226 नॉमयल मोि Normal Mode
Mode of vibration at which all the masses in a structure attain maximum values of displacements
and rotations and also pass through equilibrium positions simultaneously
227 ओवरसटरगथ Overstrength
Strength considering all factors that may cause its increase eg steel strength being higher than
the specified characteristic strength effect of strain hardening in steel with large strains and
concrete strength being higher than specified characteristic value
228 ररसाोस कमी कारक Response Reduction Factor R
The factor by which the actual lateral force that would be generated if the structure were to
remain elastic during the most severe shaking that is likely at that site shall be reduced to obtain
the design lateral force
229 ररसाोस सकटर म Response Spectrum
The representation of the maximum response of idealized single degree freedom system having
certain period and damping during that earthquake The maximum response is plotted against the
undamped natural period and for various damping values and can be expressed in terms of
maximum absolute acceleration maximum relative velocity or maximum relative displacement
230 तमटटी परोफ़ाइल फकटर Soil Profile Factor S
A factor used to obtain the elastic acceleration spectrum depending on the soil profile below the
foundation of structure
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अधयाय Chapter ndash 3
भको प क बार म About Earthquake
31 भको प Earthquake
Vibrations of earthrsquos surface caused by waves coming from a source of disturbance inside the
earth are described as earthquakes
Earthquake is a natural phenomenon occurring with all uncertainties
During the earthquake ground motions occur in a random fashion both horizontally and
vertically in all directions radiating from epicentre
These cause structures to vibrate and induce inertia forces on them
32 तकन कारणो ो स िोिा ि भको प What causes Earthquake
Earthquakes may be caused by
Tectonic activity
Volcanic activity
Land-slides and rock-falls
Rock bursting in a mine
Nuclear explosions
33 तववियतनक गतितवतध Tectonic Activity
Tectonic activity pertains to geological formation of the bedrock in the earthrsquos crust characterized
by structural features such as dislocation distortion faults folding thrusts volcanoes directly
involved in the earth movement
As engineers we are interested in earthquakes that are large enough and close enough (to the
structure) to cause concern for structural safety- usually caused by tectonic activity
Earth (Fig 31) consists of following segments ndash
solid inner core (radius ~1290km) that consists of heavy
metals (eg nickel and iron)
liquid outer core(thickness ~2200km)
stiffer mantle(thickness ~2900km) that has ability to flow
and
crust(thickness ~5 to 40km) that consists of light
materials (eg basalts and granites)
At the Core the temperature is estimated to be ~2500degC the
pressure ~4 million atmospheres and density ~135 gmcc
this is in contrast to ~25degC 1 atmosphere and 15 gmcc on the surface of the Earth
Fig 31 Inside the Earth
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Due to prevailing high temperature and pressure gradients between the Crust and the Core the
local convective currents in mantle (Fig 32) are developed These convection currents result in a
circulation of the earthrsquos mass hot molten lava comes out and the cold rock mass goes into the
Earth The mass absorbed eventually melts under high temperature and pressure and becomes a
part of the Mantle only to come out again from another location
Near the bottom of the crust horizontal component currents impose shear stresses on bottom of
crust causing movement of plates on earthrsquos surface The movement causes the plates to move
apart in some places and to converge in others
34 तववियतनक पलट का तसदाोि Theory of Plate Tectonics
Tectonic Plates Basic hypothesis of plate tectonics is that the earthrsquos surface consists of a
number of large intact blocks called plates or tectonic plates and these plates move with respect
to each other due to the convective flows of Mantle material which causes the Crust and some
portion of the Mantle to slide on the hot molten outer core The major plates are shown in
Fig 33
The earthrsquos crust is divided into six continental-sized plates (African American Antarctic
Australia-Indian Eurasian and Pacific) and about 14 of sub-continental size (eg Carribean
Cocos Nazca Philippine etc) Smaller platelets or micro-plates also have broken off from the
larger plates in the vicinity of many of the major plate boundaries
Fig 32 Convention current in mantle
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Fig 33 The major tectonic plates mid-oceanic ridges trenches and transform faults of
the earth Arrows indicate the directions of plate movement
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The relative deformation between plates occurs only in narrow zones near their boundaries
These deformations are
1 Aseismic deformation This deformation of the plates occurs slowly and continuously
2 Seismic deformation This deformation occurs with sudden outburst of energy in the form of
earthquakes
The boundaries are (i) Convergent (ii) Divergent (iii) Transform
Convergent boundary Sometimes the plate in the front is slower Then the plate behind it
comes and collides (and mountains are formed) This type of inter-plate interaction is the
convergent boundary (Fig 34)
Divergent boundary Sometimes two plates move away from one another (and rifts are
created) This type of inter-plate interaction is the divergent boundary (Fig 35)
Transform boundary Sometimes two plates move side-by-side along the same direction or in
opposite directions This type of inter-plate interaction is the transform boundary (Fig 36)
Since the deformation occurs predominantly at the boundaries between the plates it would be
expected that the locations of earthquakes would be concentrated near plate boundaries The map
of earthquake epicentres shown in Fig 37 provides strong support to confirm the theory of plate
tectonics The dots represent the epicentres of significant earthquakes It is apparent that the
locations of the great majority of earthquakes correspond to the boundaries between plates
Fig 34 Convergent Boundary
Fig 35 Divergent Boundary
Fig 36 Transform Boundary
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Fig 37 Worldwide seismic activity
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35 लचीला ररबाउोि तसदाोि Elastic Rebound Theory
Earth crust for some reason is moving in opposite
directions on certain faults This sets up elastic
strains in the rocks in the region near this fault As
the motion goes on the stresses build up in the
rocks until the stresses are large enough to cause
slip between the two adjoining portions of rocks
on either side A rupture takes place and the
strained rock rebounds back due to internal stress
Thus the strain energy in the rock is relieved
partly or fully (Fig 38)
Fault The interface between the plates where the movement has taken place is called fault
Slip When the rocky material along the interface of the plates in the Earthrsquos Crust reaches its
strength it fractures and a sudden movement called slip takes place
The sudden slip at the fault causes the earthquake A violent shaking of the Earth during
which large elastic strain energy released spreads out in the form of seismic waves that travel
through the body and along the surface of the
Earth
After elastic rebound there is a readjustment and
reapportion of the remaining strains in the region
The stress grows on a section of fault until slip
occurs again this causes yet another even though
smaller earthquake which is termed as aftershock
The aftershock activity continues until the
stresses are below the threshold level everywhere
in the rock
After the earthquake is over the process of strain build-up at this modified interface between the
tectonic plates starts all over again This is known as the Elastic Rebound Theory (Fig 39)
36 भको प और दोष क परकार Types of Earthquakes and Faults
Inter-plate Earthquakes Most earthquakes occurring along the boundaries of the tectonic
plates are called Inter-plate Earthquakes (eg 1897
Assam (India) earthquake)
Intra-plate Earthquakes Numbers of earthquakes
occurring within the plate itself but away from the
plate boundaries are called Intra-plate Earthquakes
(eg 1993 Latur (India) earthquake)
Note In both types of earthquakes the slip
generated at the fault during earthquakes is along
Fig 310 Type of Faults
Fig 38 Elastic Strain Build-Up and Brittle Rupture
Fig 39 Elastic Rebound Theory
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both vertical and horizontal directions (called Dip Slip) and lateral directions (called Strike
Slip) with one of them dominating sometimes (Fig 310)
37 जमीन कस तिलिी ि How the Ground shakes
Seismic waves Large strain energy released during an earthquake travels as seismic waves in all
directions through the Earthrsquos layers reflecting and refracting at each interface (Fig 311)
There are of two types of waves 1) Body Waves
2) Surface Waves
Body waves are of two types
a) Primary Waves (P-Wave)
b) Secondary Wave (S-Wave)
Surface waves are of two types namely
a) Love Waves
b) Rayleigh Waves
Body Waves Body waves have spherical wave front They consist of
Primary Waves (P-waves) Under P-waves [Fig 311(a)] material particles undergo
extensional and compressional strains along direction of energy transmission These waves
are faster than all other types of waves
Secondary Waves (S-waves) Under S-waves [Fig 311(b)] material particles oscillate at
Fig 311 Arrival of Seismic Waves at a Site
Fig 311(a) Motions caused by Primary Waves
Fig 311(b) Motions caused by Secondary Waves
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right angles to direction of energy transmission This type of wave shears the rock particle to
the direction of wave travel Since the liquid has no shearing resistance these waves cannot
pass through liquids
Surface Waves Surface waves have cylindrical wave front They consist of
Love Waves In case of Love waves [Fig 311(c)] the displacement is transverse with no
vertical or longitudinal components (ie similar to secondary waves with no vertical
component) Particle motion is restricted to near the surface Love waves being transverse
waves these cannot travel in liquids
Rayleigh Waves Rayleigh waves [Fig 311(d)] make a material particle oscillate in an
elliptic path in the vertical plane with horizontal motion along direction of energy
transmission
Note Primary waves are fastest followed in sequence by Secondary Love and Rayleigh waves
38 भको प या भको पी खिरो ो का परभाव Effects of Earthquake or Seismic Hazards
Basic causes of earthquake-induced damage are
Ground shaking
Structural hazards
Liquefaction
Ground failure Landslides
Tsunamis and
Fire
Fig 311(c) Motions caused by Love Waves
Fig 311(d) Motions caused by Rayleigh Waves
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381 जमीन को पन Ground shaking
Ground shaking can be considered to be the most important of all seismic hazards because all
the other hazards are caused by ground shaking
When an earthquake occurs seismic waves radiate away from the source and travel rapidly
through the earthrsquos crust
When these waves reach the ground surface they produce shaking that may last from seconds
to minutes
The strength and duration of shaking at a particular site depends on the size and location of
the earthquake and on the characteristics of the site
At sites near the source of a large earthquake ground shaking can cause tremendous damage
Where ground shaking levels are low the other seismic hazards may be low or nonexistent
Strong ground shaking can produce extensive damage from a variety of seismic hazards
depending upon the characteristics of the soil
The characteristics of the soil can greatly influence the nature of shaking at the ground
surface
Soil deposits tend to act as ldquofiltersrdquo to seismic waves by attenuating motion at certain
frequencies and amplifying it at others
Since soil conditions often vary dramatically over short distances levels of ground shaking
can vary significantly within a small area
One of the most important aspects of geotechnical earthquake engineering practice involves
evaluation of the effects of local soil conditions on strong ground motion
382 सोरचनातमक खिर Structural Hazards
Without doubt the most dramatic and memorable images of earthquake damage are those of
structural collapse which is the leading cause of death and economic loss in many
earthquakes
As the earth vibrates all buildings on the ground surface will respond to that vibration in
varying degrees
Earthquake induced accelerations velocities and displacements can damage or destroy a
building unless it has been designed and constructed or strengthened to be earthquake
resistant
The effect of ground shaking on buildings is a principal area of consideration in the design of
earthquake resistant buildings
Seismic design loads are extremely difficult to determine due to the random nature of
earthquake motions
Structures need not collapse to cause death and damage Falling objects such as brick facings
and parapets on the outside of a structure or heavy pictures and shelves within a structure
have caused casualties in many earthquakes Interior facilities such as piping lighting and
storage systems can also be damaged during earthquakes
However experiences from past strong earthquakes have shown that reasonable and prudent
practices can keep a building safe during an earthquake
Over the years considerable advancement in earthquake-resistant design has moved from an
emphasis on structural strength to emphases on both strength and ductility In current design
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practice the geotechnical earthquake engineer is often consulted for providing the structural
engineer with appropriate design ground motions
383 दरवीकरण Liquefaction
In some cases earthquake damage have occurred when soil deposits have lost their strength and
appeared to flow as fluids This phenomenon is termed as liquefaction In liquefaction the
strength of the soil is reduced often drastically to the point where it is unable to support
structures or remain stable Because it only occurs in saturated soils liquefaction is most
commonly observed near rives bays and other bodies of water
Soil liquefaction can occur in low density saturated sands of relatively uniform size The
phenomenon of liquefaction is particularly important for dams bridges underground pipelines
and buildings standing on such ground
384 जमीन तवफलिा लि सलाइि Ground Failure Land slides
1) Earthquake-induced ground Failure has been observed in the form of ground rupture along
the fault zone landslides settlement and soil liquefaction
2) Ground rupture along a fault zone may be very limited or may extend over hundreds of
kilometers
3) Ground displacement along the fault may be horizontal vertical or both and can be
measured in centimetres or even metres
4) A building directly astride such a rupture will be severely damaged or collapsed
5) Strong earthquakes often cause landslides
6) In a number of unfortunate cases earthquake-induced landslides have buried entire towns
and villages
7) Earthquake-induced landslides cause damage by destroying buildings or disrupting bridges
and other constructed facilities
8) Many earthquake-induced landslides result from liquefaction phenomenon
9) Others landslides simply represent the failures of slopes that were marginally stable under
static conditions
10) Landslide can destroy a building the settlement may only damage the building
385 सनामी Tsunamis
1) Tsunamis or seismic sea waves are generally produced by a sudden movement of the ocean
floor
2) Rapid vertical seafloor movements caused by fault rupture during earthquakes can produce
long-period sea waves ie Tsunamis
3) In the open sea tsunamis travel great distances at high speeds but are difficult to detect ndash
they usually have heights of less than 1 m and wavelengths (the distance between crests) of
several hundred kilometres
4) As a tsunami approaches shore the decreasing water depth causes its speed to decrease and
the height of the wave to increase
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5) As the water waves approach land their velocity decreases and their height increases from
5 to 8 m or even more
6) In some coastal areas the shape of the seafloor may amplify the wave producing a nearly
vertical wall of water that rushes far inland and causes devastating damage
7) Tsunamis can be devastating for buildings built in coastal areas
386 अति Fire
When the fire following an earthquake starts it becomes difficult to extinguish it since a strong
earthquake is accompanied by the loss of water supply and traffic jams Therefore the
earthquake damage increases with the earthquake-induced fire in addition to the damage to
buildings directly due to earthquakes
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17
अधयाय Chapter ndash 4
भको पी जोन और भको प का मापन Seismic Zone and Measurement of Earthquake
41 भको पी जोन Seismic Zone
Due to convective flow of mantle material crust of Earth and some portion of mantle slide on hot
molten outer core This sliding of Earthrsquos mass takes place in pieces called Tectonic Plates The
surface of the Earth consists of seven major tectonic plates (Fig 41)
They are
1 Eurasian Plate
2 Indo-Australian Plate
3 Pacific Plate
4 North American Plate
5 South American Plate
6 African Plate
7 Antarctic Plate
India lies at the northwestern end of the Indo Australian Plate (Fig 42) This Plate is colliding
against the huge Eurasian Plate and going under the Eurasian Plate Three chief tectonic sub-
regions of India are
the mighty Himalayas along the north
the plains of the Ganges and other rivers and
the peninsula
Most earthquakes occur along the Himalayan plate boundary (these are inter-plate earthquakes)
but a number of earthquakes have also occurred in the peninsular region (these are intra-plate
earthquakes)
Fig 41 Major Tectonic Plates on the Earthrsquos surface
Fig 42 Geographical Layout and Tectonic Plate
Boundaries in India
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Bureau of Indian Standards [IS1893 (part ndash 1) 2002] based on various scientific inputs from a
number of agencies including earthquake data supplied by Indian Meteorological Department
(IMD) has grouped the country into four seismic zones viz Zone II III IV and V Of these
Zone V is rated as the most seismically prone region while Zone II is the least (Fig 43)
Indian Seismic code (IS 18932002) divides the country into four seismic zones based on the
expected intensity of shaking in future earthquake The four zones correspond to areas that have
potential for shaking intensity on MSK scale as shown in the table
Seismic Zone Intensity on MSK scale of total area
II (Low intensity zone) VI (or less) 43
III (Moderate intensity zone) VII 27
IV (Severe intensity zone) VIII 18
V (Very Severe intensity zone) IX (and above) 12
Fig 43 Map showing Seismic Zones of India [IS 1893 (Part 1) 2002]
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42 भको प का मापन Measurement of Earthquake
421 मापन उपकरण Measuring Instruments
Seismograph The instrument that measures earthquake shaking is known as a seismograph
(Fig 44) It has three components ndash
Sensor ndash It consists of pendulum mass
string magnet and support
Recorder ndash It consists of drum pen and
chart paper
Timer ndash It consists of the motor that rotates
the drum at constant speed
Seismoscopes Some instruments that do not
have a timer device provide only the maximum
extent (or scope) of motion during the
earthquake
Digital instruments The digital instruments using modern computer technology records the
ground motion on the memory of the microprocessor that is in-built in the instrument
Note The analogue instruments have evolved over time but today digital instruments are more
commonly used
422 मापन क सकल Scale of Measurement
The Richter Magnitude Scale (also called Richter scale) assigns a magnitude number to quantify
the energy released by an earthquake Richter scale is a base 10 logarithmic scale which defines
magnitude as the logarithm of the ratio of the amplitude of the seismic wave to an arbitrary minor
amplitude
The magnitude M of an Earthquake is defined as
M = log10 A - log10 A0
Where
A = Recorded trace amplitude for that earthquake at a given distance as written by a
standard type of instrument (say Wood Anderson instrument)
A0 = Same as A but for a particular earthquake selected as standard
This number M is thus independent of distance between the epicentre and the station and is a
characteristic of the earthquake The standard shock has been defined such that it is low enough
to make the magnitude of most of the recorded earthquakes positive and is assigned a magnitude
of zero Thus if A = A0
Fig 44 Schematic of Early Seismograph
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M = log10 A0 - log10 A0 = 0
Standard shock of magnitude zero It is defined as one that records peak amplitude of one
thousandths of a millimetre at a distance of 100 km from the epicentre
1) Zero magnitude does not mean that there is no earthquake
2) Magnitude of an earthquake can be a negative number also
3) An earthquake that records peak amplitude of 1 mm on a standard seismograph at 100 km
will have its magnitude as
M = log10 (1) - log10 (10-3
)= 0 ndash (-3) = 3
Magnitude of a local earthquake It is defined as the logarithm to base 10 of the maximum
seismic wave amplitude (in thousandths of a mm) recorded on Wood Anderson seismograph at a
distance of 100 kms from the earthquake epicentre
1) With increase in magnitude by 10 the energy released by an earthquake increases by a
factor of about 316
2) A magnitude 80 earthquake releases about 316 times the energy released by a magnitude
70 earthquake or about 1000 times the energy released by a 60 earthquake
3) With increase in magnitude by 02 the energy released by the earthquake doubles
43 भको प पररमाण सकल क परकार Types of Earthquake Magnitude Scales
Several scales have historically been described as the ldquoRitcher Scalerdquo The Ritcher local
magnitude (ML) is the best known magnitude scale but it is not always the most appropriate scale
for description of earthquake size The Ritcher local magnitude does not distinguish between
different types of waves
At large epicentral distances body waves have usually been attenuated and scattered sufficiently
that the resulting motion is dominated by surface waves
Other magnitude scales that base the magnitude on the amplitude of a particular wave have been
developed They are
a) Surface Wave Magnitude (MS)
b) Body Wave Magnitude (Mb)
c) Moment Magnitude (Mw)
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431 सिि लिर पररमाण Surface Wave Magnitude (MS)
The surface wave magnitude (Gutenberg and Ritcher 1936) is a worldwide magnitude scale
based on the amplitude of Rayleigh waves with period of about 20 sec The surface wave
magnitude is obtained from
MS = log A + 166 log Δ + 20
Where A is the maximum ground displacement in micrometers and Δ is the epicentral distance of
the seismometer measured in degrees (3600 corresponding to the circumference of the earth)
The surface wave magnitude is most commonly used to describe the size of shallow (less than
about 70 km focal depth) distant (farther than about 1000 km) moderate to large earthquakes
432 बॉिी लिर पररमाण Body Wave Magnitude (Mb)
For deep-focus earthquakes surface waves are often too small to permit reliable evaluation of the
surface wave magnitude The body wave magnitude (Gutenberg 1945) is a worldwide magnitude
scale based on the amplitude of the first few cycles of p-waves which are not strongly influenced
by the focal depth (Bolt 1989) The body wave magnitude can be expressed as
Mb = log A ndash log T + 001Δ + 59
Where A is the p-wave amplitude in micrometers and T is the period of the p-wave (usually
about one sec)
Saturation
For strong earthquakes the measured
ground-shaking characteristics become
less sensitive to the size of the
earthquake than the smaller earthquakes
This phenomenon is referred to as
saturation (Fig 45)
The body wave and the Ritcher local
magnitudes saturate at magnitudes of 6
to 7 and the surface wave magnitude
saturates at about Ms = 8
To describe the size of a very large
earthquake a magnitude scale that does
not depend on ground-shaking levels
and consequently does not saturate
would be desirable
Fig 45 Saturation of various magnitude scale Mw (Moment
Magnitude) ML (Ritcher Local Magnitude) MS (Surface Wave
Magnitude) mb (Short-period Body Wave Magnitude) mB
(Long-period Body Wave Magnitude) and MJMA (Japanese
Meteorological Agency Magnitude)
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433 पल पररमाण Moment Magnitude (Mw)
The only magnitude scale that is not subject to saturation is the moment magnitude
The moment magnitude is given by
Mw = [(log M0)15] ndash 107
Where M0 is the seismic moment in dyne-cm
44 भको प िीवरिा Earthquake Intensity
Earthquake magnitude is simply a measure of the size of the earthquake reflecting the elastic
energy released by the earthquake It is usually referred by a certain real number on the Ritcher
scale (eg magnitude 65 earthquake)
On the other hand earthquake intensity indicates the extent of shaking experienced at a given
location due to a particular earthquake It is usually referred by a Roman numeral on the
Modified Mercalli Intensity (MMI) scale as given below
I Not felt except by a very few under especially favourable circumstances
II Felt by only a few persons at rest especially on upper floors of buildings delicately
suspended objects may swing
III Felt quite noticeably indoors especially on upper floors of buildings but many people
do not recognize it as an earthquake standing motor cars may rock slightly vibration
like passing of truck duration estimated
IV During the day felt indoors by many outdoors by few at night some awakened
dishes windows doors disturbed walls make cracking sound sensation like heavy
truck striking building standing motor cars rocked noticeably
V Felt by nearly everyone many awakened some dishes windows etc broken a few
instances of cracked plaster unstable objects overturned disturbances of trees piles
and other tall objects sometimes noticed pendulum clocks may stop
VI Felt by all many frightened and run outdoors some heavy furniture moved a few
instances of fallen plaster or damaged chimneys damage slight
VII Everybody runs outdoors damage negligible in buildings of good design and
construction slight to moderate in well-built ordinary structures considerable in
poorly built or badly designed structures some chimneys broken noticed by persons
driving motor cars
VIII Damage slight in specially designed structures considerable in ordinary substantial
buildings with partial collapse great in poorly built structures panel walls thrown out
of frame structures fall of chimneys factory stacks columns monuments walls
heavy furniture overturned sand and mud ejected in small amounts changes in well
water persons driving motor cars disturbed
IX Damage considerable in specially designed structures well-designed frame structures
thrown out of plumb great in substantial buildings with partial collapse buildings
shifted off foundations ground cracked conspicuously underground pipes broken
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X Some well-built wooden structures destroyed most masonry and frame structures
destroyed with foundations ground badly cracked rails bent landslides considerable
from river banks and steep slopes shifted sand and mud water splashed over banks
XI Few if any (masonry) structures remain standing bridges destroyed broad fissures in
ground underground pipelines completely out of service earth slumps and land slips
in soft ground rails bent greatly
XII Damage total practically all works of construction are damaged greatly or destroyed
waves seen on ground surface lines of sight and level are destroyed objects thrown
into air
441 MSK िीवरिा सकल MSK Intensity Scale
The MSK intensity scale is quite comparable to the Modified Mercalli intensity scale but is more
convenient for application in field and is widely used in India In assigning the MSK intensity
scale at a site due attention is paid to
Type of Structures (Table ndash A)
Percentage of damage to each type of structure (Table ndash B)
Grade of damage to different types of structures (Table ndash C)
Details of Intensity Scale (Table ndash D)
The main features of MSK intensity scale are as follows
Table ndash A Types of Structures (Buildings)
Type of
Structures
Definitions
A Building in field-stone rural structures unburnt ndash brick houses clay houses
B Ordinary brick buildings buildings of large block and prefabricated type half
timbered structures buildings in natural hewn stone
C Reinforced buildings well built wooden structures
Table ndash B Definition of Quantity
Quantity Percentage
Single few About 5 percent
Many About 50 percent
Most About 75 percent
Table ndash C Classification of Damage to Buildings
Grade Definitions Descriptions
G1 Slight damage Fine cracks in plaster fall of small pieces of plaster
G2 Moderate damage Small cracks in plaster fall of fairly large pieces of plaster
pantiles slip off cracks in chimneys parts of chimney fall down
G3 Heavy damage Large and deep cracks in plaster fall of chimneys
G4 Destruction Gaps in walls parts of buildings may collapse separate parts of
the buildings lose their cohesion and inner walls collapse
G5 Total damage Total collapse of the buildings
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Table ndash D Details of Intensity Scale
Intensity Descriptions
I Not noticeable The intensity of the vibration is below the limits of sensibility
the tremor is detected and recorded by seismograph only
II Scarcely noticeable
(very slight)
Vibration is felt only by individual people at rest in houses
especially on upper floors of buildings
III Weak partially
observed only
The earthquake is felt indoors by a few people outdoors only in
favourable circumstances The vibration is like that due to the
passing of a light truck Attentive observers notice a slight
swinging of hanging objects somewhat more heavily on upper
floors
IV Largely observed The earthquake is felt indoors by many people outdoors by few
Here and there people awake but no one is frightened The
vibration is like that due to the passing of a heavily loaded truck
Windows doors and dishes rattle Floors and walls crack
Furniture begins to shake Hanging objects swing slightly Liquid
in open vessels are slightly disturbed In standing motor cars the
shock is noticeable
V Awakening
a) The earthquake is felt indoors by all outdoors by many Many
people awake A few run outdoors Animals become uneasy
Buildings tremble throughout Hanging objects swing
considerably Pictures knock against walls or swing out of
place Occasionally pendulum clocks stop Unstable objects
overturn or shift Open doors and windows are thrust open
and slam back again Liquids spill in small amounts from
well-filled open containers The sensation of vibration is like
that due to heavy objects falling inside the buildings
b) Slight damages in buildings of Type A are possible
c) Sometimes changes in flow of springs
VI Frightening
a) Felt by most indoors and outdoors Many people in buildings
are frightened and run outdoors A few persons loose their
balance Domestic animals run out of their stalls In few
instances dishes and glassware may break and books fall
down Heavy furniture may possibly move and small steeple
bells may ring
b) Damage of Grade 1 is sustained in single buildings of Type B
and in many of Type A Damage in few buildings of Type A
is of Grade 2
c) In few cases cracks up to widths of 1cm possible in wet
ground in mountains occasional landslips change in flow of
springs and in level of well water are observed
VII Damage of buildings
a) Most people are frightened and run outdoors Many find it
difficult to stand The vibration is noticed by persons driving
motor cars Large bells ring
b) In many buildings of Type C damage of Grade 1 is caused in
many buildings of Type B damage is of Grade 2 Most
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buildings of Type A suffer damage of Grade 3 few of Grade
4 In single instances landslides of roadway on steep slopes
crack inroads seams of pipelines damaged cracks in stone
walls
c) Waves are formed on water and is made turbid by mud stirred
up Water levels in wells change and the flow of springs
changes Sometimes dry springs have their flow resorted and
existing springs stop flowing In isolated instances parts of
sand and gravelly banks slip off
VIII Destruction of
buildings
a) Fright and panic also persons driving motor cars are
disturbed Here and there branches of trees break off Even
heavy furniture moves and partly overturns Hanging lamps
are damaged in part
b) Most buildings of Type C suffer damage of Grade 2 and few
of Grade 3 Most buildings of Type B suffer damage of Grade
3 Most buildings of Type A suffer damage of Grade 4
Occasional breaking of pipe seams Memorials and
monuments move and twist Tombstones overturn Stone
walls collapse
c) Small landslips in hollows and on banked roads on steep
slopes cracks in ground up to widths of several centimetres
Water in lakes becomes turbid New reservoirs come into
existence Dry wells refill and existing wells become dry In
many cases change in flow and level of water is observed
IX General damage of
buildings
a) General panic considerable damage to furniture Animals run
to and fro in confusion and cry
b) Many buildings of Type C suffer damage of Grade 3 and a
few of Grade 4 Many buildings of Type B show a damage of
Grade 4 and a few of Grade 5 Many buildings of Type A
suffer damage of Grade 5 Monuments and columns fall
Considerable damage to reservoirs underground pipes partly
broken In individual cases railway lines are bent and
roadway damaged
c) On flat land overflow of water sand and mud is often
observed Ground cracks to widths of up to 10 cm on slopes
and river banks more than 10 cm Furthermore a large
number of slight cracks in ground falls of rock many
landslides and earth flows large waves in water Dry wells
renew their flow and existing wells dry up
X General destruction of
building
a) Many buildings of Type C suffer damage of Grade 4 and a
few of Grade 5 Many buildings of Type B show damage of
Grade 5 Most of Type A have destruction of Grade 5
Critical damage to dykes and dams Severe damage to
bridges Railway lines are bent slightly Underground pipes
are bent or broken Road paving and asphalt show waves
b) In ground cracks up to widths of several centimetres
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sometimes up to 1m Parallel to water courses occur broad
fissures Loose ground slides from steep slopes From river
banks and steep coasts considerable landslides are possible
In coastal areas displacement of sand and mud change of
water level in wells water from canals lakes rivers etc
thrown on land New lakes occur
XI Destruction
a) Severe damage even to well built buildings bridges water
dams and railway lines Highways become useless
Underground pipes destroyed
b) Ground considerably distorted by broad cracks and fissures
as well as movement in horizontal and vertical directions
Numerous landslips and falls of rocks The intensity of the
earthquake requires to be investigated specifically
XII Landscape changes
a) Practically all structures above and below ground are greatly
damaged or destroyed
b) The surface of the ground is radically changed Considerable
ground cracks with extensive vertical and horizontal
movements are observed Falling of rock and slumping of
river banks over wide areas lakes are dammed waterfalls
appear and rivers are deflected The intensity of the
earthquake requires to be investigated specially
442 तवतभनन सकलो ो की िीवरिा मलो ो की िलना Comparison of Intensity Values of
Different Scales
443 तवतभनन पररमाण और िीवरिा क भको प का परभाव Effect of Earthquake of various
Magnitude and Intensity
The following describes the typical effects of earthquakes of various magnitudes near the
epicenter The values are typical only They should be taken with extreme caution since intensity
and thus ground effects depend not only on the magnitude but also on the distance to the
epicenter the depth of the earthquakes focus beneath the epicenter the location of the epicenter
and geological conditions (certain terrains can amplify seismic signals)
Fig 45 Comparison of Intensity Values of Different Scales
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Magnitude Description Mercalli
intensity
Average earthquake effects Average
frequency of
occurrence
(estimated)
10-19 Micro I Micro earthquakes not felt or felt rarely
Recorded by seismographs
Continualseveral
million per year
20-29 Minor I to II Felt slightly by some people No damage to
buildings
Over one million
per year
30-39 III to IV Often felt by people but very rarely causes
damage Shaking of indoor objects can be
noticeable
Over 100000 per
year
40-49 Light IV to VI Noticeable shaking of indoor objects and
rattling noises Felt by most people in the
affected area Slightly felt outside
Generally causes none to minimal damage
Moderate to significant damage very
unlikely Some objects may fall off shelves
or be knocked over
10000 to 15000
per year
50-59 Moderate VI to
VIII
Can cause damage of varying severity to
poorly constructed buildings At most none
to slight damage to all other buildings Felt
by everyone
1000 to 1500 per
year
60-69 Strong VII to X Damage to a moderate number of well-built
structures in populated areas Earthquake-
resistant structures survive with slight to
moderate damage Poorly designed
structures receive moderate to severe
damage Felt in wider areas up to hundreds
of mileskilometers from the epicenter
Strong to violent shaking in epicentral area
100 to 150 per
year
70-79 Major VIII or
Greater
Causes damage to most buildings some to
partially or completely collapse or receive
severe damage Well-designed structures
are likely to receive damage Felt across
great distances with major damage mostly
limited to 250 km from epicenter
10 to 20 per year
80-89 Great Major damage to buildings structures
likely to be destroyed Will cause moderate
to heavy damage to sturdy or earthquake-
resistant buildings Damaging in large
areas Felt in extremely large regions
One per year
90 and
greater
At or near total destruction ndash severe damage
or collapse to all buildings Heavy damage
and shaking extends to distant locations
Permanent changes in ground topography
One per 10 to 50
years
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45 भको प तनगरानी और सवाओो क तलए एजतसयो ो Agencies for Earthquake Monitoring and
Services
Centre for Seismology (CS) in Indian Meteorological Department (IMD) under Ministry of
Earth Sciences is nodal agency of Government of India dealing with various activities in
the field of seismology and allied disciplines and is responsible for monitoring seismic
activity in and around the country
The major activities currently being pursued by the Centre for Seismology (CS) include
a) Earthquake monitoring on 24X7 basis including real time seismic monitoring for early
warning of tsunamis
b) Operation and maintenance of national seismological network and local networks
c) Seismological data centre and information services
d) Seismic hazard and risk related studies
e) Field studies for aftershock swarm monitoring site response studies
f) Earthquake processes and modelling etc
These activities are being managed by various unitsgroups of the Centre for Seismology
(CS) as detailed below
1) Centre for Seismology (CS) is maintaining a country wide National Seismological
Network (NSN) consisting of a total of 82 seismological stations spread over the
entire length and breadth of the country This includes
a) 16-station V-SAT based digital seismic telemetry system around National Capital
Territory (NCT) of Delhi
b) 20-station VSAT based real time seismic monitoring network in North East region
of the country
(c) 17-station Real Time Seismic Monitoring Network (RTSMN) to monitor and
report large magnitude under-sea earthquakes capable of generating tsunamis on
the Indian coastal regions
2) The remaining stations are of standalone analog type
3) A Control Room is in operation on a 24X7 basis at premises of IMD Headquarters in
New Delhi with state-of-the art facilities for data collection processing and
dissemination of information to the concerned user agencies
4) India represented by CSIMD is a permanent Member of the International
Seismological Centre (ISC) UK
5) Seismological Bulletins of CSIMD are shared regularly with International
Seismological Centre (ISC) UK for incorporation in the ISCs Monthly Seismological
Bulletins which contain information on earthquakes occurring all across the globe
6) Towards early warning of tsunamis real-time continuous seismic waveform data of
three IMD stations viz Portblair Minicoy and Shillong is shared with global
community through IRIS (Incorporated Research Institutions of Seismology)
Washington DC USA
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अधयाय Chapter ndash 5
भवन म भको प परतिरोध म सधार क तलए सामानय तसदाोि General Principle for improving Earthquake Resistance in Building
51 िलकापन Lightness
Since the earthquake force is a function of mass the building should be as light as possible
consistent with structural safety and functional requirements Roofs and upper storeys of
buildings in particular should be designed as light as possible
52 तनमायण की तनरोिरिा Continuity of Construction
As far as possible all parts of the building should be tied together in such a manner that
the building acts as one unit
For integral action of building roof and floor slabs should be continuous throughout as
far as possible
Additions and alterations to the structures should be accompanied by the provision of
positive measures to establish continuity between the existing and the new construction
53 परोजककटोग एवो ससिि पाटटयस Projecting and Suspended Parts
Projecting parts should be avoided as far as possible If the projecting parts cannot be
avoided they should be properly reinforced and firmly tied to the main structure
Ceiling plaster should preferably be avoided When it is unavoidable the plaster should
be as thin as possible
Suspended ceiling should be avoided as far as possible Where provided they should be
light and adequately framed and secured
54 भवन की आकति Shape of Building
In order to minimize torsion and stress concentration the building should have a simple
rectangular plan
It should be symmetrical both with respect to mass and rigidity so that the centre of mass
and rigidity of the building coincide with each other
It will be desirable to use separate blocks of rectangular shape particularly in seismic
zones V and IV
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55 सतवधा जनक तबकडोग लआउट Preferred Building Layouts
Buildings having plans with shapes like L T E and Y shall preferably be separated into
rectangular parts by providing separation sections at appropriate places Typical examples are
shown in Fig 51
56 तवतभनन तदशाओो म शककत Strength in Various Directions
The structure shall have adequate strength against earthquake effects along both the horizontal
axes considering the reversible nature of earthquake forces
57 नी ोव Foundations
For the design of foundations the provisions of IS 1904 1986 in conjunctions with IS
1893 1984 shall generally be followed
The sub-grade below the entire area of the building shall preferably be of the same type of
the soil Wherever this is not possible a suitably located separation or crumple section shall
be provided
Loose fine sand soft silt and expansive clays should be avoided If unavoidable the
building shall rest either on a rigid raft foundation or on piles taken to a firm stratum
However for light constructions the following measures may be taken to improve the soil
on which the foundation of the building may rest
a) Sand piling and b) Soil stabilization
Structure shall not be founded on loose soil which will subside or liquefy during an
earthquake resulting in large differential settlement
58 छि एवो मोतजल Roofs and Floors
581 सपाट छि या फशय Flat roof or floor
Flat roof or floor shall not preferably be made of terrace of ordinary bricks supported on steel
timber or reinforced concrete joists nor they shall be of a type which in the event of an
earthquake is likely to be loosened and parts of all of which may fall If this type of construction
cannot be avoided the joists should be blocked at ends and bridged at intervals such that their
spacing is not altered during an earthquake
Fig 51 Typical Shapes of Building with Separation Sections [IS 4326 1993]
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582 ढलान वाली छि Pitched Roofs
For pitched roofs corrugated iron or asbestos sheets should be used in preference to
country Allahabad or Mangalore tiles or other loose roofing units
All roofing materials shall be properly tied to the supporting members
Heavy roofing materials should generally be avoided
583 सोवि छि Pent Roofs
All roof trusses should be supported on and fixed to timber band reinforced concrete band or
reinforced brick band The holding down bolts should have adequate length as required for
earthquake and wind forces
Where a trussed roof adjoins a masonry gable the ends of the purlins should be carried on and
secured to a plate or bearer which should be adequately bolted to timber reinforced concrete or
reinforced brick band at the top of gable end masonry
- At tie level all the trusses and the gable end should be provided with diagonal braces in plan
so as to transmit the lateral shear due to earthquake force to the gable walls acting as shear
walls at the ends
NOTE ndash Hipped roof in general have shown better structural behaviour during earthquakes than gable
ended roofs
584 जक मिराब Jack Arches
Jack arched roofs or floors where used should be provided with mild steel ties in all spans along
with diagonal braces in plan to ensure diaphragm actions
59 सीतढ़याो Staircases
The interconnection of the stairs with the adjacent floors should be appropriately treated by
providing sliding joints at the stairs to eliminate their bracing effect on the floors
Ladders may be made fixed at one end and freely resting at the other
Large stair halls shall preferably be separated from rest of the building by means of
separation or crumple section
Three types of stair construction may be adopted as described below
591 अलग सीतढ़याो Separated Staircases
One end of the staircase rests on a wall and the other end is carried by columns and beams which
have no connection with the floors The opening at the vertical joints between the floor and the
staircase may be covered either with a tread plate attached to one side of the joint and sliding on
the other side or covered with some appropriate material which could crumple or fracture during
an earthquake without causing structural damage
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The supporting members columns or walls are
isolated from the surrounding floors by means of
separation or crumple sections A typical
example is shown in Fig 52
592 तबलट-इन सीतढ़याो Built-in Staircase
When stairs are built monolithically with floors they can be protected against damage by
providing rigid walls at the stair opening An arrangement in which the staircase is enclosed by
two walls is given in Fig 53 (a) In such cases the joints as mentioned in respect of separated
staircases will not be necessary
The two walls mentioned above enclosing the staircase shall extend through the entire height of
the stairs and to the building foundations
Fig 53 (a) Rigidly Built-In Staircase [IS 4326 1993]
Fig 52 Separated Staircase
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593 सलाइतिोग जोड़ो ो वाली सीतढ़याो Staircases with Sliding Joints
In case it is not possible to provide rigid walls around stair openings for built-in staircase or to
adopt the separated staircases the staircases shall have sliding joints so that they will not act as
diagonal bracing (Fig 53 (b))
510 बॉकस परकार तनमायण Box Type Construction
This type of construction consists of prefabricated or in-situ masonry wall along with both the
axes of the building The walls support vertical loads and also act as shear walls for horizontal
loads acting in any direction All traditional masonry construction falls under this category In
prefabricated wall construction attention should be paid to the connections between wall panels
so that transfer of shear between them is ensured
511 अति सरकषा Fire Safety
Fire frequently follows an earthquake and therefore buildings should be constructed to make
them fire resistant in accordance with the provisions of relevant Indian Standards for fire safety
The relevant Indian Standards are IS 1641 1988 IS 1642 1989 IS 1643 1988 IS 1644 1988
and IS 1646 1986
Fig 53 (b) Staircase with Sliding Joint
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अधयाय Chapter ndash 6
भको प क दौरान आर सी भवनो ो क परदशयन पर सटरकचरल अतनयतमििाओो का परभाव Effect of Structural Irregularities on Performance of RC Buildings during Earthquakes
61 सटरकचरल अतनयतमििाओो का परभाव Effect of Structural Irregularities
There are numerous examples of past earthquakes in which the cause of failure of reinforced
concrete building has been ascribed to irregularities in configurations
Irregularities are mainly categorized as
(i) Horizontal Irregularities
(ii) Vertical Irregularities
62 कषतिज अतनयतमििाएो Horizontal Irregularities
Horizontal irregularities refer to asymmetrical plan shapes (eg L- T- U- F-) or discontinuities
in the horizontal resisting elements (diaphragms) such as cut-outs large openings re-entrant
corners and other abrupt changes resulting in torsion diaphragm deformations stress
concentration
Table ndash 61 Definitions of Irregular Buildings ndash Plan Irregularities (Fig 61)
S
No
Irregularity Type and Description
(i) Torsion Irregularity To be considered when floor diaphragms are rigid in their own
plan in relation to the vertical structural elements that resist the lateral forces Torsional
irregularity to be considered to exist when the maximum storey drift computed with
design eccentricity at one end of the structures transverse to an axis is more than 12
times the average of the storey drifts at the two ends of the structure
Fig 61 (a)
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(ii) Re-entrant Corners Plan configurations of a structure and its lateral force resisting
system contain re-entrant corners where both projections of the structure beyond the re-
entrant corner are greater than 15 percent of its plan dimension in the given direction
Fig 61 (b)
(iii) Diaphragm Discontinuity Diaphragms with abrupt discontinuities or variations in
stiffness including those having cut-out or open areas greater than 50 percent of the
gross enclosed diaphragm area or changes in effective diaphragm stiffness of more than
50 percent from one storey to the next
Fig 61 (c)
(iv) Out-of-Plane Offsets Discontinuities in a lateral force resistance path such as out-of-
plane offsets of vertical elements
Fig 61 (d)
(v) Non-parallel Systems The vertical elements
resisting the lateral force are not parallel to or
symmetric about the major orthogonal axes or the
lateral force resisting elements
Fig 61 (e)
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63 ऊरधायधर अतनयतमििाएो Vertical Irregularities
Vertical irregularities referring to sudden change of strength stiffness geometry and mass result
in irregular distribution of forces and or deformation over the height of building
Table ndash 62 Definition of Irregular Buildings ndash Vertical Irregularities (Fig 62)
S
No
Irregularity Type and Description
(i) a) Stiffness Irregularity ndash Soft Storey A soft storey is one in which the lateral stiffness is
less than 70 percent of that in the storey above or less than 80 percent of the average lateral
stiffness of the three storeys above
b) Stiffness Irregularity ndash Extreme Soft Storey A extreme soft storey is one in which the
lateral stiffness is less than 60 percent of that in the storey above or less than 70 percent of
the average stiffness of the three storeys above For example buildings on STILTS will fall
under this category
Fig 62 (a)
(ii) Mass Irregularity Mass irregularity shall be considered to exist where the seismic weight
of any storey is more than 200percent of that of its adjacent storeys The irregularity need
not be considered in case of roofs
Fig 62 (b)
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(iii) Vertical Geometric Irregularity Vertical geometric irregularity shall be considered to
exist where the horizontal dimension of the lateral force resisting system in any storey is
more than150 percent of that in its adjacent storey
Fig 62 (c)
(iv) In-Plane Discontinuity in Vertical Elements Resisting Lateral Force A in-plane offset of
the lateral force resisting elements greater than the length of those elements
Fig 62 (d)
(v) Discontinuity in Capacity ndash Weak Storey A weak storey is one in which the storey lateral
strength is less than 80 percent of that in the storey above The storey lateral strength is the
total strength of all seismic force resisting elements sharing the storey shear in the
considered direction
64 भवन तवनयास अतनयतमििाएो ndash सरसकयमए ववशलषण एव तनदमन क उपमय Building
Irregularities ndash Problems Analysis and Remedial Measures
The influence of irregularity on performance of building during earthquakes is presented to
account for the effects of these irregularities in analysis of problems and their solutions along
with the design
Vertical Geometric Irregularity when L2gt15 L1
In-Plane Discontinuity in Vertical Elements Resisting Weak Storey when Filt08Fi+ 1
Lateral Force when b gta
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Architectural problems Structural problems Remedial measures
Extreme heightdepth ratio
High overturning forces large drift causing non-structural damage foundation stability
Revive properties or special structural system
Extreme plan area Built-up large diaphragm forces Subdivide building by seismic joints
Extreme length depth ratio
Built-up of large lateral forces in perimeter large differences in resistance of two axes Experience greater variations in ground movement and soil conditions
Subdivide building by seismic joints
Variation in perimeter strength-stiffness
Torsion caused by extreme variation in strength and stiffness
Add frames and disconnect walls or use frames and lightweight walls
False symmetry Torsion caused by stiff asymmetric core Disconnect core or use frame with non-structural core walls
Re-entrant corners Torsion stress concentrations at the notches
Separate walls uniform box centre box architectural relief diagonal reinforcement
Mass eccentricities Torsion stress concentrations Reprogram or add resistance around mass to balance resistance and mass
Vertical setbacks and reverse setbacks
Stress concentration at notch different periods for different parts of building high diaphragm forces to transfer at setback
Special structural systems careful dynamic analysis
Soft storey frame Causes abrupt changes of stiffness at point of discontinuity
Add bracing add columns braced
Variation in column stiffness
Causes abrupt changes of stiffness much higher forces in stiffer columns
Redesign structural system to balance stiffness
Discontinuous shear wall Results in discontinuities in load path and stress concentration for most heavily loaded elements
Primary concern over the strength of lower level columns and connecting beams that support the load of discontinuous frame
Weak column ndash strong beam
Column failure occurs before beam short column must try and accommodate storey height displacement
Add full walls to reduce column forces or detach spandrels from columns or use light weight curtain wall with frame
Modification of primary structure
Most serious when masonry in-fill modifies structural concept creation of short stiff columns result in stress concentration
Detach in-fill or use light-weight materials
Building separation (Pounding)
Possibility of pounding dependent on building period height drift distance
Ensure adequate separation assuming opposite building vibrations
Coupled Incompatible deformation between walls and links
Design adequate link
Random Openings Seriously degrade capacity at point of maximum force transfer
Careful designing adequate space for reinforcing design
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अधयाय Chapter ndash 7
भवन की िायनातमक तवशषिाएा Dynamic Characteristics of Building
71 िायनातमक तवशषिाएा Dynamic Characteristics
Buildings oscillate during earthquake shaking The oscillation causes inertia force to be induced
in the building The intensity and duration of oscillation and the amount of inertia force induced
in a building depend on features of buildings called dynamic characteristics of building
The important dynamic characteristics of buildings are
a) Modes of Oscillation
b) Damping
A mode of oscillation of a building is defined by associated Natural Period and Deformed Shape
in which it oscillates Every building has a number of natural frequencies at which it offers
minimum resistance to shaking induced by external effects (like earthquakes and wind) and
internal effects(like motors fixed on it) Each of these natural frequencies and the associated
deformation shape of a building constitute a Natural Mode of Oscillation
The mode of oscillation with the smallest natural frequency (and largest natural period) is called
the Fundamental Mode the associated natural period T1is called the Fundamental Natural
Period
72 पराकतिक अवतध Natural Period
Natural Period (Tn) of a building is the time taken by it to undergo one complete cycle of
oscillation It is an inherent property of a building controlled by its mass m and stiffness k These
three quantities are related by
Its unit is second (s)
73 पराकतिक आवततत Natural Frequency
The reciprocal (1Tn) of natural period of a building is called the Natural Frequency fn its unit is
Hertz (Hz)
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74 पराकतिक अवतध को परभातवि करन वाल कारक Factors influencing Natural Period
741 कठोरिा का परभाव Effect of Stiffness Stiffer buildings have smaller natural period
742 दरवयमान का परभाव Effect of Mass Heavier buildings have larger natural period
743 कॉलम अतभतवनयास का परभाव Effect of Column Orientation Buildings with larger
column dimension oriented in the direction reduces the translational natural period of oscillation
in that direction
Fig 72 Effect of Mass
Fig 71 Effect of Stiffness
Fig 73 Effect of Column Orientation
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744 भवन की ऊो चाई का परभाव Effect of Building Height Taller buildings have larger
natural period
745 Unreinforced तचनाई भराव का परभाव Effect of Unreinforced Masonry Infills Natural
Period of building is lower when the stiffness contribution of URM infill is considered
Fig 75 Effect of Building Height
Fig 74 Effect of Building Height
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75 Mode आकति Mode Shape
Mode shape of oscillation associated with a natural period of a building is the deformed shape of
the building when shaken at the natural period Hence a building has as many mode shapes as
the number of natural periods
The deformed shape of the building associated with oscillation at fundamental natural period is
termed its first mode shape Similarly the deformed shapes associated with oscillations at
second third and other higher natural periods are called second mode shape third mode shape
and so on respectively
Fundamental Mode Shape of Oscillation
As shown in Fig 76 there are three basic modes of oscillation namely
1 Pure translational along X-direction
2 Pure translational along Y-direction and
3 Pure rotation about Z-axis
Regular buildings
These buildings have pure mode shapesThe Basic modes of oscillation ie two translational and
one rotational mode shapes
Irregular buildings
These buildings that have irregular geometry non-uniform distribution of mass and stiffness in
plan and along the height have mode shapes which are a mixture of these pure mode shapes
Each of these mode shapes is independent implying it cannot be obtained by combining any or
all of the other mode shapes
a) Fundamental and two higher translational modes of oscillation along X-direction of a
five storey benchmark building First modes shape has one zero crossing of the un-deformed
position second two and third three
Fig 76 Basic modes of oscillation
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b) Diagonal modes of oscillation First three modes of oscillation of a building symmetric in
both directions in plan first and second are diagonal translational modes and third rotational
c) Effect of modes of oscillation on column bending Columns are severely damaged while
bending about their diagonal direction
Fig 77 Fundamental and two higher translational modes of oscillation
along X-direction of a five storey benchmark building
Fig 78 Diagonal modes of oscillation
Fig 79 Effect of modes of oscillation on column bending
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76 Mode आकतियो ो को परभातवि करन वाल कारक Factors influencing Mode Shapes
761 Effect of relative flexural stiffness of structural elements Fundamental translational
mode shape changes from flexural-type to shear-type with increase in beam flexural stiffness
relative to that of column
762 Effect of axial stiffness of vertical members Fundamental translational mode shape
changes from flexure-type to shear-type with increase in axial stiffness of vertical members
Fig 710 Effect of relative flexural stiffness of structural elements
Fig 711 Effect of axial stiffness of vertical members
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763 Effect of degree of fixity at member ends Lack of fixity at beam ends induces flexural-
type behaviour while the same at column bases induces shear-type behaviour to the fundamental
translational mode of oscillation
Fig 712 Effect of degree of fixity at member ends
764 Effect of building height Fundamental translational mode shape of oscillation does not
change significantly with increase in building height unlike the fundamental translational natural
period which does change
Fig 713 Effect of building height
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765 Influence of URM Infill Walls in Mode Shape of RC frame Buildings Mode shape of
a building obtained considering stiffness contribution of URM is significantly different from that
obtained without considering the same
77 सोरचना की परतितकरया Response of Structure
The earthquakes cause vibratory motion which is cyclic about the equilibrium The structural
response is vibratory (Dynamic) and it is cyclic about the equilibrium position of structure The
fundamental natural frequency of most civil engineering structures lie in the range of 01 sec to
30 sec or so This is also the range of frequency content of earthquake-generated ground
motions Hence the ground motion imparts considerable amount of energy to the structures
Initially the structure responds elastically to the ground motion however as its yield capacity is
exceeded the structure responds in an inelastic manner During the inelastic response stiffness
and energy dissipation properties of the structure are modified
Response of the structure to a given strong ground motion depends not only on the properties of
input ground motion but also on the structural properties
78 तिजाइन सकटर म Design Spectrum
The design spectrum is a design specification which is arrived at by considering all aspects The
design spectrum may be in terms of acceleration velocity or displacement
Fig 714 Influence of URM Infill Walls in Mode Shape of RC frame Buildings
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Since design spectrum is a specification for design it cannot be viewed in isolation without
considering the other factors that go into the design process One must concurrently specify
a) The procedure to calculate natural period of the structure
b) The damping to be used for a given type of structure
c) The permissible stresses and strains load factors etc
Unless this information is part of a design spectrum the design specification is incomplete
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अधयाय Chapter ndash 8
डिजमइन पमशवा बलो क तनधमारण क ललए कोि आधमररि िरीकम Code based Procedure for Determination of Design Lateral Loads
81 भको पी तिजाइन की तफलोसफ़ी Philosophy of Seismic Design
Design of earthquake effect is not termed as Earthquake Proof Design Actual forces that appear
on structure during earthquake are much greater than the design forces Complete protection
against earthquake of all size is not economically feasible and design based alone on strength
criteria is not justified Earthquake demand is estimated only based on concept of probability of
exceedance Design of earthquake effect is therefore termed as Earthquake Resistant Design
against the probable value of demand
Maximum Considered Earthquake (MCE) The earthquake corresponding to the Ultimate
Safety Requirement is often called as Maximum Considered Earthquake
Design Basis Earthquake (DBE) It is defined as the Maximum Earthquake that reasonably can
be expected to experience at the site during lifetime of structure
The philosophy of seismic design is to ensure that structures possess at least a minimum strength
to
(i) resist minor (lt DBE) which may occur frequently without damage
(ii) resist moderate earthquake (DBE) without significant structural damage through some
non-structural damage
(iii) resist major earthquake (MCE) without collapse
82 भको पी तवशलषण क तलए िरीक Methods for Seismic Analysis
The response of a structure to ground vibrations is a function of the nature of foundation soil
materials form size and mode of construction of structures and duration and characteristics of
ground motion Code specifies design forces for structures standing on rock or firm soils which
do not liquefy or slide due to loss of strength during ground motion
Analysis is carried out by
a- Dynamic analysis procedure [Clause 78 of IS 1893 (Part I) 2002]
b- Simplified method referred as Lateral Force Procedure [Clause 75 of IS 1893 (Part I)
2002] also recognized as Equivalent Lateral Force Procedure or Equivalent Static
Procedure in the literature
The main difference between the equivalent lateral force procedure and dynamic analysis
procedure lies in the magnitude and distribution of lateral forces over the height of the buildings
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In the dynamic analysis procedure the lateral forces are based on the properties of the natural
vibration modes of the building which are determined by the distribution of mass and stiffness
over height In the equivalent lateral force procedures the magnitude of forces is based on an
estimation of the fundamental period and on the distribution of forces as given by simple
formulae appropriate for regular buildings
83 िायनातमक तवशलषण Dynamic Analysis
Dynamic analysis shall be performed to obtain the design seismic force and its distribution to
different levels along the height of the building and to the various lateral load resisting elements
for the following buildings
a) Regular buildings ndash Those greater than 40 m in height in Zones IV and V and those greater
than 90 m in height in Zones II and III Modelling as per Para 7845 of IS 1893 (Part 1)
2002 can be used
b) Irregular buildings (as defined in Table ndash 61 and Table ndash 62 of Chapter - 6) ndash All framed
buildings higher than 12m in Zones IV and V and those greater than 40m in height in Zones
II and III
84 पारशय बल परतकरया Lateral Force Procedure
The random earthquake ground motions which cause the structure to vibrate can be resolved in
any three mutually perpendicular directions The predominant direction of ground vibration is
usually horizontal
The codes represent the earthquake-induced inertia forces in the form of design equivalent static
lateral force This force is called as the Design Seismic Base Shear VB VB remains the primary
quantity involved in force-based earthquake-resistant design of buildings
The Design Seismic Base Shear VB is given by
Where Ah = Design horizontal seismic coefficient for a structure
=
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Z = Zone Factor
It is for the Maximum Considered Earthquake (MCE) and service life of structure in a zone
Generally Design Basis Earthquake (DBE) is half of Maximum Considered Earthquake
(MCE) The factor 2 in the denominator of Z is used so as to reduce the MCE zone factor to
the factor for DBE
The value of Ah will not be taken less than Z2 whatsoever the value of IR
The value of Zone Factor is given in Table ndash 81
Table ndash 81 Zone Factor Z[IS 1893 (Part 1) 2002]
Seismic Zone II III IV V
Seismic Intensity Low Moderate Severe Very Severe
Zone Factor Z 010 016 024 036
I = Importance Factor
Value of importance factor depends upon the functional use of the structures characterized
by hazardous consequences of its failure post-earthquake functional needs historical value
or economic importance (as given in Table ndash 82)
Table ndash 82 Importance Factors I [IS 1893 (Part 1) 2002]
S
No
Structure Importance
Factor
(i) Important service and community buildings such as hospitals schools
monumental structures emergency buildings like telephone exchange
television stations radio stations railway stations fire station buildings
large community halls like cinemas assembly halls and subway stations
power stations
15
(ii) AU other buildings 10
Note
1 The design engineer may choose values of importance factor I greater than those
mentioned above
2 Buildings not covered in S No (i) and (ii) above may be designed for higher value of I
depending on economy strategy considerations like multi-storey buildings having
several residential units
3 This does not apply to temporary structures like excavations scaffolding etc of short
duration
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R = Response Reduction Factor
To make normal buildings economical design code allows some damage for reducing the
cost of construction This philosophy is introduced with the help of Response reduction
factor R
The ratio (IR) shall not be greater than 10
Depending on the perceived seismic damage performance of the structure by ductile or brittle
deformations the values of R1)
for buildings are given in Table ndash 83 below
Table ndash 83 Response Reduction Factor1)
R for Building Systems [IS 1893 (Part 1) 2002]
S No Lateral Load Resisting System R Building Frame Systems (i) Ordinary RC moment-resisting frame ( OMRF )
2) 30
(ii) Special RC moment-resisting frame ( SMRF )3)
50 (iii) Steel frame with
a) Concentric braces 40 b) Eccentric braces 50
(iv) Steel moment resisting frame designed as per SP 6 (6) 50 Building with Shear Walls
4)
(v) Load bearing masonry wall buildings5)
a) Unreinforced 15 b) Reinforced with horizontal RC bands 25 c) Reinforced with horizontal RC bands and vertical bars at cornersof
rooms and jambs of openings 30
(vi) Ordinary reinforced concrete shear walls6)
30 (vii) Ductile shear walls
7) 40
Buildings with Dual Systems8)
(viii) Ordinary shear wall with OMRF 30 (ix) Ordinary shear wall with SMRF 40 (x) Ductile shear wall with OMRF 45 (xi) Ductile shear wall with SMRF 50 1) The values of response reduction factor are to be used for buildings with lateral load resisting
elements and not just for the lateral load resisting elements built in isolation 2) OMRF (Ordinary Moment-Resisting Frame) are those designed and detailed as per IS 456 or
IS 800 but not meeting ductile detailing requirement as per IS 13920 or SP 6 (6) respectively 3) SMRF (Special Moment-Resisting Frame) defined in 4152
As per 4152 SMRF is a moment-resisting frame specially detailed to provide ductile behaviour and comply with the requirements given in IS 4326 or IS 13920 or SP 6 (6)
4) Buildings with shear walls also include buildings having shear walls and frames but where a) frames are not designed to carry lateral loads or b) frames are designed to carry lateral loads but do not fulfil the requirements of lsquodual
systemsrsquo 5) Reinforcement should be as per IS 4326 6) Prohibited in zones IV and V 7) Ductile shear walls are those designed and detailed as per IS 13920 8) Buildings with dual systems consist of shear walls ( or braced frames ) and moment resisting
frames such that a) the two systems are designed to resist the total design force in proportion to their lateral
stiffness considering the interaction of the dual system at all floor levels and b) the moment resisting frames are designed to independently resist at least 25 percent of the
design seismic base shear
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Sag = Average Response Acceleration Coefficient
Net shaking of a building is a combined effect of the energy carried by the earthquake at
different frequencies and the natural period (T) of the building Code reflects this by
introducing a structural flexibility factor (Sag) also termed as Design Acceleration
Coefficient
Design Acceleration Coefficient (Sag) corresponding to 5 damping for different soil
types normalized to Peak Ground Acceleration (PAG) corresponding to natural period (T)
of structure considering soil structure interaction given by Fig 81 and associated expression
given below
Table ndash 84 gives multiplying factors for obtaining spectral values for various other damping
Table ndash 84 Multiplying Factors for Obtaining Values for Other Damping [IS 1893 (Part 1) 2002]
Damping () 0 2 5 7 10 15 20 25 30
Factors 320 140 100 090 080 070 060 055 050
85 को पन की मौतलक पराकतिक अवतध Fundamental Natural Period of Vibration
The approximate fundamental natural period of vibration (Ta)in seconds of a moment-resisting
frame building without brick infill panels may be estimated by the empirical expression
Ta = 0075 h075
for RC frame building
= 0085 h075
for steel frame building
Where h = Height of building in m This excludes the basement storeys where
basement walls are connected with the ground floor deck or fitted between
the building columns But it includes the basement storeys when they are
not so connected
Fig 81 Response Spectra for Rock and Soil Sitesfor5 Damping [IS 1893 (Part 1) 2002]
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53
The approximate fundamental natural period of vibration (Ta) in seconds of all other buildings
including moment-resisting frame buildings with brick infill panels may be estimated by the
empirical expression
Where h = Height of building in m as defined above
d = Base dimension of the building at the plinth level in m along the
considered direction of the lateral force
86 तिजाइन पारशय बल Design Lateral Force
The total design lateral force or design seismic base shear (VB) along any principal direction shall
be determined by the following expression
Where Ah= Design horizontal acceleration spectrum value as per 642 using the
fundamental natural period Ta as per 76 in the considered direction of
vibration and
W= Seismic weight of the building
The design lateral force shall first be computed for the building as a whole This design lateral
force shall then be distributed to the various floor levels
The overall design seismic force thus obtained at each floor level shall then be distributed to
individual lateral load resisting elements depending on the floor diaphragm action
87 तिजाइन बल का तविरण Distribution of Design Force
871 Vertical Distribution of Base Shear to Different Floor Levels
The Design Seismic Base Shear (VB) as computed above shall be distributed along the height of
the building as per the following expression
Where
Qi= Design lateral force at floor i
Wi = Seismic weight of floor i
hi = Height of floor i measured from base and
n= Number of storeys in the building is the number of levels at which the masses are
located
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872 Distribution of Horizontal Design Lateral Force to Different Lateral Force Resisting
Elements
1 In case of buildings whose floors are capable of providing rigid horizontal diaphragm
action the total shear in any horizontal plane shall be distributed to the various vertical
elements of lateral force resisting system assuming the floors to be infinitely rigid in the
horizontal plane
2 In case of building whose floor diaphragms cannot be treated as infinitely rigid in their
own plane the lateral shear at each floor shall be distributed to the vertical elements
resisting the lateral forces considering the in-plane flexibility of the diaphragms
Notes
1 A floor diaphragm shall be considered to be flexible if it deforms such that the maximum
lateral displacement measured from the chord of the deformed shape at any point of the
diaphragm is more than 15 times the average displacement of the entire diaphragm
2 Reinforced concrete monolithic slab-beam floors or those consisting of prefabricated
precast elements with topping reinforced screed can be taken rigid diaphragms
88 तिजाइन उदािरण Design Example ndash To determine Base Shear and its distribution
along Height of Building
Exercise ndash 1 Determine the total base shear as per IS 1893(Part 1)2002 and distribute the base
shear along the height of building to be used as school building in Bhuj Gujrat and founded on
Medium Soil Basic parameters for design of building are as follows
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55
ELEVATION
Solution
Basic Data
Following basic data is considered for analysis
i) Grade of Concrete M-25
ii) Grade of Steel Fe ndash 415 Tor Steel
iii) Density of Concrete 25 KNm3
iv) Density of Brick Wall 20 KNm3
v) Live Load for Roof 15 KNm2
vi) Live Load for Floor 50 KNm2
vii) Slab Thickness 150 mm
viii) Beam Size
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56
(a) 500 m Span 250 mm X 600 mm
(b) 400 m Span 250 mm X 550 mm
(c) 200 m Span 250 mm X 400 mm
ix) Column Size
(a) For 500 m Span 300 mm X 600 mm
(b) For 200 m Span 300 mm X 500 mm
Load Calculations
1 Dead Load Building is of G+4 Storeys
Approximate Covered Area of Building on GF = 30 X 8 = 240 m2
Approximate Covered Area of 1st 2
nd 3
rd amp 4
th Floor = 240 m
2
Total Floor Area = 5 X 240 = 1200 m2
Roof Area = 1 X 240 = 240 m2
(I) Slab
Self Wt of Slab = 015 X 25 = 375 KNm2
Wt of Floor Finish = 125 KNm2
------------------------------
Total = 500 KNm2
Dead Load of Slab per Floor = 240 X 5 = 1200 KN
Dead Load of Slab on Roof = 240 X 5 = 1200 KN
(II) Beam
Wt per m of 250 X 600 mm beam = 025 X 060 X 25 = 375 KNm
Wt per m of 250 X 550 mm beam = 025 X 055 X 25 = 344 KNm
Wt per m of 250 X 400 mm beam = 025 X 040 X 25 = 250 KNm
Weight of Beam per Floor
= (2 X 30 X 375) + (4 X 6 + 30) X 344 + (2 X 6 X 250)
= 225 + 18576 + 30 = 44076 KN [Say 44100 KN]
(III) Column
Wt per m of 300 X 600 mm column = 030 X 060 X 25 = 450 KNm
Wt per m of 300 X 500 mm column = 030 X 050 X 25 = 375 KNm
Weight of Column per Floor
= (12 X 3 X 450) + (6 X 3 X 375)
= 162 + 6750 = 22950 KN [Say 23000 KN]
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57
Walls
250 mm thick wall (including plaster) are provided Assuming 20 opening in the
wall ndash
Wt of Wall per m = 025 X 080 X 20 X 250
Wall Thickness Reduction Density Clear Height
= 1000 KNm
Wt of Parapet Wall per m = 0125 X 20 X 100 = 250 KNm
Wall Thickness Density Clear Height
Wt of Wall per Floor = 1000 X [30 X 3 + 2 X 2] = 940 KN
Wt of Wall at Roof = 250 X [30 X 2 + 8 X 2] = 190 KN
Total Dead Load ndash
(i) For Floor = Slab + Beam + Column + Wall
= 1200 + 441 + 230 + 940 = 2811 KN
(ii) For Roof = 1200 + 441 + 190 = 1831 KN
Slab Beam Parapet
2 Live Load Live Load on Floor = 40 KNm2
As per Table ndash 8 in Cl 731 of IS 1893 (Part 1)2002 ldquoage of Imposed Load to be
considered in Seismic Weight calculationrdquo
(i) Up to amp including 300 KNm2 = 25
(ii) Above 300 KNm2 = 50
Live Load on Floors to be = 200 KNm2 [ie 50 of 40 KNm
2]
considered for Earthquake Force
As per Cl 732 of IS 1893 (Part 1)2002 for calculating the design seismic force of the
structure the imposed load on roof need not be considered
Therefore Live Load on Roof = 000 KN
Seismic Weight due to Live Load
(i) For Floor = 240 X 2 = 480 KN
(ii) For Roof = 000 KN
3 Seismic Weight of Building
As per Cl 74 of IS 1893 (Part 1)2002
(i) For Floor = DL of Floor + LL on Floor
= 2811 + 480 = 3291 KN
(ii) For Roof = 1831 + 000 = 1831 KN
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Total Seismic Weight of Building = 5 X 3291 + 1 X 1831
W = 18286 KN
4 Determination of Base Shear
As per Cl 75 of IS 1893 (Part 1)2002 VB = Ah W
Where
VB = Base Shear
Ah = Design Horizontal Acceleration Spectrum
=
W = Seismic Wt of Building
Total height of Building above Ground Level = 1500 m
As per Cl 76 of IS 1893 (Part 1)2002 Fundamental Natural Period of Vibration for RC
Frame Building is
Ta = 0075 h075
= 0075 (15)075
= 0572 Sec
Average Response Acceleration Coefficient = 25
for 5 damping and Type II soil
Bhuj Gujrat is in Seismic Zone V
As per Table ndash 2 of IS 1893 (Part 1)2002
Zone Factor Z = 036
As per Table ndash 6 of IS 1893 (Part 1)2002
Impedance Factor I = 150
As per Table ndash 7 of IS 1893 (Part 1)2002
Response Reduction Factor for Ordinary R = 300
RC Moment-resisting Frame (OMRF) Building
Ah =
= (0362) X (1530) X (25)
= 0225
Base Shear VB = Ah W
= 0225 X 18286
= 411435 KN [Say 411400 KN]
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5 Vertical Distribution of Base Shear to Different Floors Levels
As per Cl 771 of IS 1893 (Part 1)2002
Where
Qi= Design lateral force at floor i
Wi = Seismic weight of floor i
hi = Height of floor i measured from base and
n= Number of storeys in the building is the number of levels at which the masses are
located
VB = 4114 KN
Storey
No
Mass
No
Wi hi Wi hi2
f =
Qi = VB x f
(KN)
Vi
(KN)
Roof 1 1831 18 593244 0268 1103 1103
4th
Floor 2 3291 15 740475 0333 1370 2473
3rd
Floor 3 3291 12 473904 0213 876 3349
2nd
Floor 4 3291 9 266571 0120 494 3843
1st Floor 5 3291 6 118476 0053 218 4061
Ground 6 3291 3 29619 0013 53 4114
= 2222289
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60
अधयाय Chapter ndash 9
ढााचागि सोरचना का तनमायण Construction of Framed Structure
91 गरतवाकषयण लोतिोग और भको प लोतिोग म आर सी तबकडोग का वयविार Behaviour of RC
Building in Gravity Loading and Earthquake Loading
In recent times reinforced concrete buildings have become common in India particularly in
towns and cities A typical RC building consists of horizontal members (beams and slabs) and
vertical members (columns and walls) The system is supported by foundations that rest on
ground The RC frame participates in resisting the gravity and earthquake forces as illustrated in
Fig 91
Gravity Loading
1 Load due to self weight and contents on buildings cause RC frames to bend resulting in
stretching and shortening at various locations
2 Tension is generated at surfaces that stretch
and compression at those that shorten
3 Under gravity loads tension in the beams is
at the bottom surface of the beam in the
central location and is at the top surface at
the ends
Earthquake Loading
1 It causes tension on beam and column faces
at locations different from those under
gravity loading the relative levels of this
tension (in technical terms bending
moment) generated in members are shown
in Figure
2 The level of bending moment due to
earthquake loading depends on severity of
shaking and can exceed that due to gravity
loading
3 Under strong earthquake shaking the beam
ends can develop tension on either of the
top and bottom faces
4 Since concrete cannot carry this tension
steel bars are required on both faces of
beams to resist reversals of bending
moment
5 Similarly steel bars are required on all faces of columns too
Fig 91 Earthquake shaking reverses tension and
compression in members ndash reinforcement is
required on both faces of members
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92 परबतलि को करीट इमारिो ो पर कषतिज भको प का परभाव Effect of Horizontal Earthquake Force
on RC Buildings
Earthquake shaking generates inertia forces in the building which are proportional to the
building mass Since most of the building mass is present at floor levels earthquake-induced
inertia forces primarily develop at the floor
levels These forces travel downwards -
through slab and beams to columns and walls
and then to the foundations from where they
are dispersed to the ground (Fig 92)
As inertia forces accumulate downwards from
the top of the building the columns and walls
at lower storeys experience higher earthquake-
induced forces and are therefore designed to be
stronger than those in storeys above
93 कषमिा तिजाइन सोकलपना Capacity Design Concept
(i) Let us take two bars of same length amp Cross-sectional area
1st bar ndash Made up of Brittle Material
2nd
bar ndash Made up of Ductile Material
(ii) Pull both the bars until they break
(iii) Plot the graph of bar force F versus bar
elongation Graph will be as given in Fig
93
(iv) It is observed that ndash
a) Brittle bar breaks suddenly on reaching its
maximum strength at a relatively small
elongation
b) Ductile bar elongates by a large amount
before it breaks
Materials used in building construction are steel
masonry and concrete Steel is ductile material
while masonry and concrete are brittle material
Capacity design concept ensures that the brittle
element will remain elastic at all loads prior to the
failure of ductile element Thus brittle mode of
failure ie sudden failure has been prevented
Fig 92 Total horizontal earthquake force in a
building increase downwards along its height
Fig 93 Tension Test on Materials ndash ductile
versus brittle materials
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The concept of capacity design is used to ensure post-yield ductile behaviour of a structure
having both ductile and brittle elements In this method the ductile elements are designed and
detailed for the design forces Then an upper-bound strength of the ductile elements is obtained
It is then expected that if the seismic force keeps increasing a point will come when these ductile
elements will reach their upper-bound strength and become plastic Clearly it is necessary to
ensure that even at that level of seismic force the brittle elements remain safe
94 लचीलापन और ऊजाय का अपवयय Ductility and Energy Dissipation
From strength point of view overdesigned structures need not necessarily demonstrate good
ductility By ductility of Moment Resisting Frames (MRF) one refers to the capacity of the
structure and its elements to undergo large deformations without loosing either strength or
stiffness It is important for a building in a seismic zone to be resilient ie absorb the shock from
the ground and dissipate this energy uniformly throughout the structure
In MRFs the dissipation of the input seismic energy takes place in the form of flexural yielding
and resulting in the formation of plastic moment hinges Due to cyclic nature of the flexural
effects both positive and negative plastic moment hinges may be formed
95 मजबि सतोभ ndash कमजोर बीम फलोसफ़ी lsquoStrong Column ndash Weak Beamrsquo Philosophy
Because beams are usually capable of developing large ductility than columns which are
subjected to significant compressive loads many building frames are designed based on the
lsquostrong column ndash weak beamrsquo philosophy Figure shows that for a frame designed according to
the lsquostrong column ndash weak beamrsquo philosophy to form a failure mechanism many more plastic
hinges have to be formed than a
frame designed according to the
ldquoweak column ndash strong beamrsquo
philosophy The frames designed
by the former approach dissipate
greater energy before failure
When this strategy is adopted in
design damage is likely to occur
first in beams When beams are
detailed properly to have large
ductility the building as a whole
can deform by large amounts
despite progressive damage caused
due to consequent yielding of
beams
Note If columns are made weaker they suffer severe local damage at the top and bottom of a
particular storey This localized damage can lead to collapse of a building although columns at
storeys above remain almost undamaged (Fig 94)
Fig 94 Two distinct designs of buildings that result in different
earthquake performancesndashcolumns should be stronger than beams
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For a building to remain safe during earthquake shaking columns (which receive forces from
beams) should be stronger than beams and foundations (which receive forces from columns)
should be stronger than columns
96 कठोर िायाफराम तकरया Rigid Diaphragm Action
When beams bend in the vertical direction during earthquakes these thin slabs bend along with them And when beams move with columns in the horizontal direction the slab usually forces the beams to move together with it In most buildings the geometric distortion of the slab is negligible in the horizontal plane this behaviour is known as the rigid diaphragm action This aspect must be considered during design (Fig 95)
97 सॉफट सटोरी तबकडोग क साथ ndash ओपन गराउोि सटोरी तबकडोग जो तक भको प क समय कमजोर िोिी ि
Building with Soft storey ndash Open Ground Storey Building that is vulnerable in
Earthquake
The buildings that have been constructed in recent times with a special feature - the ground storey is left open for the purpose of parking ie columns in the ground storey do not have any partition walls (of either masonry or RC) between them are called open ground storey buildings or buildings on stilts
An open ground storey building (Fig 96) having only columns in the ground storey and both partition walls and columns in the upper storeys have two distinct characteristics namely
(a) It is relatively flexible in the ground storey ie the relative horizontal displacement it undergoes in the ground storey is much larger than what each of the storeys above it does This flexible ground storey is also called soft storey
(b) It is relatively weak in ground storey ie
the total horizontal earthquake force it can carry in the ground storey is significantly smaller than what each of the storeys above it can carry Thus the open ground storey may also be a weak storey
Fig 95 Floor bends with the beam but moves all
columns at that level together
Fig 96 Upper storeys of open ground storey building
move together as a single block ndash such buildings are
like inverted pendulums
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The collapse of more than a hundred RC frame buildings with open ground storeys at
Ahmedabad (~225km away from epicenter) during the 2001 Bhuj earthquake has emphasized
that such buildings are extremely vulnerable under earthquake shaking
After the collapses of RC buildings in 2001 Bhuj earthquake the Indian Seismic Code IS 1893
(Part 1) 2002 has included special design provisions related to soft storey buildings
Firstly it specifies when a building should be considered as a soft and a weak storey building
Secondly it specifies higher design forces for the soft storey as compared to the rest of the
structure
The Code suggests that the forces in the columns
beams and shear walls (if any) under the action of
seismic loads specified in the code may be
obtained by considering the bare frame building
(without any infills) However beams and
columns in the open ground storey are required to
be designed for 25 times the forces obtained
from this bare frame analysis (Fig 97)
For all new RC frame buildings the best option is
to avoid such sudden and large decrease in stiffness
andor strength in any storey it would be ideal to
build walls (either masonry or RC walls) in the
ground storey also Designers can avoid dangerous
effects of flexible and weak ground storeys by
ensuring that too many walls are not discontinued
in the ground storey ie the drop in stiffness and
strength in the ground storey level is not abrupt due
to the absence of infill walls (Fig 98)
The existing open ground storey buildings need to be strengthened suitably so as to prevent them
from collapsing during strong earthquake shaking The owners should seek the services of
qualified structural engineers who are able to suggest appropriate solutions to increase seismic
safety of these buildings
971 भरी हई दीवार In-Fill Walls
When columns receive horizontal forces at floor
levels they try to move in the horizontal direction
but masonry walls tend to resist this movement
Due to their heavy weight and thickness these
walls attract rather large horizontal forces
However since masonry is a brittle material these
walls develop cracks once their ability to carry
horizontal load is exceeded Thus infill walls act
like sacrificial fuses in buildings they develop
Fig 99 Infill walls move together with the
columns under earthquake shaking
Fig 97 Open ground storey building ndashassumptions
made in current design practice are not consistent
with the actual structure
Fig 98 Avoiding open ground storey problem ndash
continuity of walls in ground storey is preferred
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65
cracks under severe ground shaking but help share the load of the beams and columns until
cracking Earthquake performance of infill walls is enhanced by mortars of good strength
making proper masonry courses and proper packing of gaps between RC frame and masonry
infill walls (Fig 99)
98 भको प क दौरान लघ कॉलम वाली इमारिो ो का वयविार Behavior of Buildings with Short
Columns during Earthquakes
During past earthquakes reinforced concrete (RC) frame buildings that have columns of different heights within one storey suffered more damage in the shorter columns as compared to taller columns in the same storey
Two examples of buildings with short columns are shown in Fig 910 ndash (a) buildings on a sloping ground and (b) buildings with a mezzanine floor
Poor behaviour of short columns is due to the fact that in an earthquake a tall column and a short column of same cross-section move horizontally by same amount
However the short column is stiffer as compared
to the tall column and it attracts larger earthquake
force Stiffness of a column means resistance to
deformation ndash the larger is the stiffness larger is
the force required to deform it If a short column is
not adequately designed for such a large force it
can suffer significant damage during an
earthquake This behaviour is called Short Column
Effect (Fig 911)
In new buildings short column effect should be
avoided to the extent possible during architectural
design stage itself When it is not possible to avoid
short columns this effect must be addressed in
structural design The IS13920-1993for ductile
detailing of RC structures requires special
confining reinforcement to be provided over the
full height of columns that are likely to sustain
short column effect
Fig 910 Buildings with short columns ndash two
explicit examples of common occurrences
Fig 911 Short columns are stiffer and attract larger
forces during earthquakes ndash this must be accounted
for in design
Fig 912 Details of reinforcement in a building with
short column effect in some columns ndashadditional
special requirements are given in IS13920- 1993 for
the short columns
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66
The special confining reinforcement (ie closely spaced closed ties) must extend beyond the
short column into the columns vertically above and below by a certain distance as shown in
Fig 912
In existing buildings with short columns different retrofit solutions can be employed to avoid
damage in future earthquakes Where walls of partial height are present the simplest solution is
to close the openings by building a wall of full height ndash this will eliminate the short column
effect If that is not possible short columns need to be strengthened using one of the well
established retrofit techniques The retrofit solution should be designed by a qualified structural
engineer with requisite background
99 भको प परतिरोधी इमारिो ो की लचीलापन आवशयकिाएा Ductility requirements of
Earthquake Resistant Buildings
The primary members of structure such as beams and columns are subjected to stress reversals
from earthquake loads The reinforcement provided shall cater to the needs of reversal of
moments in beams and columns and at their junctions
Earthquake motion often induces forces large enough to cause inelastic deformations in the
structure If the structure is brittle sudden failure could occur But if the structure is made to
behave ductile it will be able to sustain the earthquake effects better with some deflection larger
than the yield deflection by absorption of energy Therefore besides the design for strength of
the frame ductility is also required as an essential element for safety from sudden collapse during
severe shocks
The ductility requirements will be deemed to be satisfied if the conditions given as in the
following are achieved
1 For all buildings which are more than 3 storeys in height the minimum grade of concrete
shall be M20 ( fck = 20 MPa )
2 Steel reinforcements of grade Fe 415 (IS 1786 1985) or less only shall be used
However high strength deformed steel bars produced by the thermo-mechanical treatment
process of grades Fe 500 and Fe 550 having elongation more than 145 percent and conforming
to other requirements of IS 1786 1985 may also be used for the reinforcement
910 बीम तजनह आर सी इमारिो ो म भको प बलो ो का तवरोध करन क तलए िाला जािा ि Beams that
are required to resist Earthquake Forces in RC Buildings
In RC buildings the vertical and horizontal members (ie the columns and beams) are built
integrally with each other Thus under the action of loads they act together as a frame
transferring forces from one to another
Beams in RC buildings have two sets of steel reinforcement (Fig 913) namely
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(a) long straight bars (called longitudinal bars)
placed along its length and
(b) closed loops of small diameter steel bars (called
stirrups)placed vertically at regular intervals
along its full length
Beams sustain two basic types of failures namely
(i) Flexural (or Bending) Failure
As the beam sags under increased loading it can
fail in two possible ways (Fig 914)
If relatively more steel is present on the tension
face concrete crushes in compression this is
a brittle failure and is therefore undesirable
If relatively less steel is present on the
tension face the steel yields first (it keeps
elongating but does not snap as steel has
ability to stretch large amounts before it
snaps and redistribution occurs in the beam
until eventually the concrete crushes in
compression this is a ductile failure and
hence is desirable Thus more steel on
tension face is not necessarily desirable The
ductile failure is characterized with many
vertical cracks starting from the stretched
beam face and going towards its mid-depth
(ii) Shear Failure
A beam may also fail due to shearing action A shear crack is inclined at 45deg to the horizontal it
develops at mid-depth near the support and grows towards the top and bottom faces Closed loop
stirrups are provided to avoid such shearing action Shear damage occurs when the area of these
stirrups is insufficient Shear failure is brittle and therefore shear failure must be avoided in the
design of RC beams
Longitudinal bars are provided to resist flexural
cracking on the side of the beam that stretches
Since both top and bottom faces stretch during
strong earthquake shaking longitudinal steel bars
are required on both faces at the ends and on the
bottom face at mid-length (Fig 915)
Fig 914 Two types of damage in a beam flexure
damage is preferred Longitudinal bars resist the
tension forces due to bending while vertical stirrups
resist shear forces
Fig 913 Steel reinforcement in beams ndash stirrups
prevent longitudinal bars from bending outwards
Fig 915 Location and amount of longitudinal steel
bars in beams ndash these resist tension due to flexure
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Designing a beam involves the selection of its material properties (ie grades of steel bars
and concrete) and shape and size these are usually selected as a part of an overall design
strategy of the whole building
The amount and distribution of steel to be provided in the beam must be determined by
performing design calculations as per IS 456-2000 and IS 13920-1993
911 फलकसचरल ममबसय क तलए सामानय आवशयकिाएा General Requirements for Flexural
Members
These members shall satisfy the following requirements
The member shall preferably have a width-to-depth ratio of more than 03
The width of the member shall not be less than 200 mm
The depth D of the member shall preferably be not more than 14 of the clear span
The factored axial stress on the member under earthquake loading shall not exceed 01fck
9111 अनदधयय सदढीकरण Longitudinal Reinforcement
a) The top as well as bottom reinforcement shall consist of at least two bars throughout the
member length
b) The tension steel ratio on any face at any section shall not be less than ρmin = 024 where fck
and fy are in MPa
The positive steel at a joint face must be at least equal to half the negative steel at that face
The steel provided at each of the top and bottom face of the member at any section along its
length shall be at least equal to one-fourth of the maximum negative moment steel provided
at the face of either joint It may be clarified that
redistribution of moments permitted in IS 456
1978 (clause 361) will be used only for vertical
load moments and not for lateral load moments
In an external joint both the top and the bottom
bars of the beam shall be provided with anchorage
length beyond the inner face of the column equal
to the development length in tension plus 10 times
the bar diameter minus the allowance for 90 degree
bend(s) (as shown in Fig 916) In an internal joint
both face bars of the beam shall be taken
continuously through the column
Fig 916 Anchorage of Beam Bars in an External Joint (IS 13920 1993)
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9112 अनदधयय सदढीकरण की सपलाइतसोग Splicing of longitudinal reinforcement
The longitudinal bars shall be spliced only if hoops are
provided over the entire splice length at a spacing not
exceeding 150 mm (as shown in Fig 917) The lap length
shall not be less than the bar development length in tension
Lap splices shall not be provided (a) within a joint (b)
within a distance of 2d from joint face and (c) within a
quarter length of the member where flexural yielding may
generally occur under the effect of earthquake forces Not
more than 50 percent of the bars shall be spliced at one
section
Use of welded splices and mechanical connections may also be made as per 25252 of
IS 456-1978 However not more than half the reinforcement shall be spliced at a section
where flexural yielding may take place
9113 वब सदढीकरण Web Reinforcement
Web reinforcement shall consist of vertical hoops A vertical hoop is a closed stirrup having a
135deg hook with a 10 diameter extension (but
not lt 75 mm) at each end that is embedded
in the confined core [as shown in (a) of
Fig 918] In compelling circumstances it
may also be made up of two pieces of
reinforcement a U-stirrup with a 135deg hook
and a 10 diameter extension (but not lt 75
mm) at each end embedded in the confined
core and a crosstie [as shown in (b) of Fig
918] A crosstie is a bar having a 135deg hook
with a 10 diameter extension (but not lt 75
mm) at each end The hooks shall engage
peripheral longitudinal bars
912 कॉलम तजनह आर सी इमारिो ो म भको प बलो ो का तवरोध करन क तलए िाला जािा ि Columns that are required to resist Earthquake Forces in RC Buildings
Columns the vertical members in RC buildings contain two types of steel reinforcement
namely
(a) long straight bars (called longitudinal bars) placed vertically along the length and
(b) closed loops of smaller diameter steel bars (called transverse ties) placed horizontally at
regular intervals along its full length
Fig 917 Lap Splice in Beam
(IS 13920 1993)
Fig 918 Beam Web Reinforcement (IS 13920 1993)
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Columns can sustain two types of damage namely axial-flexural (or combined compression-
bending) failure and shear failure Shear damage is brittle and must be avoided in columns by
providing transverse ties at close spacing
Closely spaced horizontal closed ties (Fig 919)
help in three ways namely
(i) they carry the horizontal shear forces
induced by earthquakes and thereby resist
diagonal shear cracks
(ii) they hold together the vertical bars and
prevent them from excessively bending
outwards(in technical terms this bending
phenomenon is called buckling) and
(iii) they contain the concrete in the column
within the closed loops The ends of the
ties must be bent as 135deg hooks Such hook
ends prevent opening of loops and
consequently bulging of concrete and
buckling of vertical bars
Construction drawings with clear details of closed ties are helpful in the effective implementation
at construction site In columns where the spacing between the corner bars exceeds 300mm the
Indian Standard prescribes additional links with 180deg hook ends for ties to be effective in holding
the concrete in its place and to prevent the buckling of vertical bars These links need to go
around both vertical bars and horizontal closed ties (Fig 920) special care is required to
implement this properly at site
Designing a column involves selection of
materials to be used (ie grades of concrete and
steel bars) choosing shape and size of the cross-
section and calculating amount and distribution
of steel reinforcement The first two aspects are
part of the overall design strategy of the whole
building The IS 13920 1993 requires columns
to be at least 300mm wide A column width of up
to 200 mm is allowed if unsupported length is less
than 4m and beam length is less than 5m
Columns that are required to resist earthquake
forces must be designed to prevent shear failure
by a skillful selection of reinforcement
Fig 919 Steel reinforcement in columns ndash closed ties
at close spacing improve the performance of column
under strong earthquake shaking
Fig 920 Extra links are required to keep the
concrete in place ndash 180deg links are necessary to
prevent the135deg tie from bulging outwards
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913 एकसीयल लोिि मबसय क तलए सामानय आवशयकिाएा General Requirements for Axial
Loaded Members
These requirements apply to frame members which have a factored axial stress in excess of
01 fck under the effect of earthquake forces
The minimum dimension of the member shall not be less than 200 mm However in frames
which have beams with centre to centre span exceeding 5 m or columns of unsupported
length exceeding 4 m the shortest dimension of the column shall not be less than 300 mm
The ratio of the shortest cross sectional dimension to the perpendicular dimension shall
preferably not be less than 04
9131 अनदधयय सदढीकरण Longitudinal Reinforcement
Lap splices shall be provided only in the central half
of the member length It should be proportioned as a
tension splice Hoops shall be provided over the
entire splice length at spacing not exceeding 150
mm centre to centre Not more than 50 percent of
the bars shall be spliced at one section
Any area of a column that extends more than 100
mm beyond the confined core due to architectural
requirements shall be detailed in the following
manner
a) In case the contribution of this area to strength
has been considered then it will have the minimum longitudinal and transverse
reinforcement as per IS 13920 1993
b) However if this area has been treated as non-structural the minimum reinforcement
requirements shall be governed by IS 456 1978 provisions minimum longitudinal and
transverse reinforcement as per IS 456 1978 (as shown in Fig 921)
9132 अनपरसथ सदढीकरण Transverse Reinforcement
Transverse reinforcement for circular columns shall consist of spiral or circular hoops In
rectangular columns rectangular hoops may be used A rectangular hoop is a closed stirrup
having a 135deg hook with a 10 diameter extension (but not lt 75 mm) at each end that is
embedded in the confined core [as shown in (A) of Fig 922]
Fig 921 Reinforcement requirement for Column with more than 100 mm projection beyond core(IS 13920 1993)
Fig 922 Transverse Reinforcement in Column (IS 13920 1993)
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The parallel legs of rectangular hoop shall be spaced not more than 300 mm centre to centre
If the length of any side of the hoop exceeds 300 mm a crosstie shall be provided [as shown
in (B) of Fig 922] Alternatively a pair of overlapping hoops may be provided within the
column [as shown in (C) of Fig 922] The hooks shall engage peripheral longitudinal bars
The spacing of hoops shall not exceed half the least lateral dimension of the column except
where special confining reinforcement is provided as per Para 915 below
914 बीम-कॉलम जोड़ जो आर सी भवनो ो म भको प बलो ो का तवरोध करि ि Beam-Column Joints
that resist Earthquakes Forces in RC Buildings
In RC buildings portions of columns that are
common to beams at their intersections are
called beam column joints (Fig 923) The
joints have limited force carrying capacity
When forces larger than these are applied
during earthquakes joints are severely
damaged Repairing damaged joints is
difficult and so damage must be avoided
Thus beam-column joints must be designed
to resist earthquake effects
Under earthquake shaking the beams adjoining a joint are subjected to moments in the same
(clockwise or counter-clockwise) direction
Under these moments the top bars in the
beam-column joint are pulled in one
direction and the bottom ones in the
opposite direction These forces are
balanced by bond stress developed between
concrete and steel in the joint region
(Fig 924)
If the column is not wide enough or if the
strength of concrete in the joint is low there
is insufficient grip of concrete on the steel
bars In such circumstances the bar slips
inside the joint region and beams loose
their capacity to carry load Further under
the action of the above pull-push forces at top and bottom ends joints undergo geometric
distortion one diagonal length of the joint elongates and the other compresses
If the column cross-sectional size is insufficient the concrete in the joint develops diagonal
cracks
Fig 923 Beam-Column Joints are critical parts of a
building ndash they need to be designed
Fig924 Pull-push forces on joints cause two
problems ndash these result in irreparable damage in joints
under strong seismic shaking
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9141 बीम-कॉलम जोड़ मजबि करन क तलए सामानय आवशयकिाएा General Requirements
for Reinforcing the Beam-Column Joint
Diagonal cracking and crushing of concrete in joint
region should be prevented to ensure good
earthquake performance of RC frame buildings
(Fig 925)
Using large column sizes is the most effective
way of achieving this
In addition closely spaced closed-loop steel ties
are required around column bars to hold
together concrete in joint region and to resist
shear forces
Intermediate column bars also are effective in
confining the joint concrete and resisting
horizontal shear forces Providing closed-loop
ties in the joint requires some extra effort
IS 13920ndash1993 recommends continuing the
transverse loops around the column bars
through the joint region
In practice this is achieved by preparing the cage of
the reinforcement (both longitudinal bars and
stirrups) of all beams at a floor level to be prepared
on top of the beam formwork of that level and
lowered into the cage (Fig 926)
However this may not always be possible
particularly when the beams are long and the entire
reinforcement cage becomes heavy
The gripping of beam bars in the joint region is
improved first by using columns of reasonably
large cross-sectional size
The Indian Standard IS 13920-1993 requires building columns in seismic zones III IV and V to
be at least 300mm wide in each direction of the cross-section when they support beams that are
longer than 5m or when these columns are taller than 4m between floors (or beams)
In exterior joints where beams terminate at columns longitudinal beam bars need to be anchored
into the column to ensure proper gripping of bar in joint The length of anchorage for a bar of
grade Fe415 (characteristic tensile strength of 415MPa) is about 50 times its diameter This
Fig 925 Closed loop steel ties in beam-column
joints ndash such ties with 135deg hooks resist the ill
effects of distortion of joints
Fig 926 Providing horizontal ties in the joints ndash
three-stage procedure is required
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length is measured from the face of the column to the end of the bar anchored in the column
(Fig 927)
In columns of small widths and when beam
bars are of large diameter (Fig 928(a)) a
portion of beam top bar is embedded in the
column that is cast up to the soffit of the
beam and a part of it overhangs It is difficult
to hold such an overhanging beam top bar in
position while casting the column up to the
soffit of the beam Moreover the vertical
distance beyond the 90ordm bend in beam bars is
not very effective in providing anchorage
On the other hand if column width is large
beam bars may not extend below soffit of the
beam (Fig 928 (b)) Thus it is preferable to
have columns with sufficient width
In interior joints the beam bars (both top and
bottom) need to go through the joint without
any cut in the joint region Also these bars
must be placed within the column bars and
with no bends
915 तवशष सीतमि सदढीकरण Special Confining Reinforcement
This requirement shall be met with unless a
larger amount of transverse reinforcement is
required from shear strength considerations
Special confining reinforcement shall be
provided over a length lsquolorsquo from each
joint face towards mid span and on
either side of any section where flexural
yielding may occur under the effect of
earthquake forces (as shown in Fig 929)
The length lsquolorsquo shall not be less than
(a) larger lateral dimension of the
member at the section where yielding
occurs
(b) 16 of clear span of the member and
(c) 450 mm
Fig 929 Column and Joint Detailing (IS 13920 1993)
Fig 927 Anchorage of beam bars in exterior
joints ndash diagrams show elevation of joint region
Fig 928 Anchorage of beam bars in interior
jointsndash diagrams (a) and (b) show cross-sectional
views in plan of joint region
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When a column terminates into a footing or mat special confining reinforcement shall extend
at least 300 mm into the footing or mat (as shown in Fig 930)
When the calculated point of contra-flexure
under the effect of gravity and earthquake
loads is not within the middle half of the
member clear height special confining
reinforcement shall be provided over the full
height of the column
Columns supporting reactions from discontinued stiff members such as walls shall be
provided with special confining reinforcement over their full height (as shown in Fig 931)
This reinforcement shall also be placed above the discontinuity for at least the development
length of the largest longitudinal bar in the column Where the column is supported on a wall
this reinforcement shall be provided
over the full height of the column it
shall also be provided below the
discontinuity for the same development
length
Special confining reinforcement shall
be provided over the full height of a
column which has significant variation
in stiffness along its height This
variation in stiffness may result due to
the presence of bracing a mezzanine
floor or a RCC wall on either side of
the column that extends only over a part
of the column height (as shown in Fig
931)
916 तवशषिः भको पीय कषतर म किरनी दीवारो ो वाली इमारिो ो का तनमायण Construction of Buildings
with Shear Walls preferably in Seismic Regions
Reinforced concrete (RC) buildings often have vertical
plate-like RC walls called Shear Walls in addition to
slabs beams and columns These walls generally start
at foundation level and are continuous throughout the
building height Their thickness can be as low as
150mm or as high as 400mm in high rise buildings
Shear walls are usually provided along both length and
width of buildings Shear walls are like vertically-
oriented wide beams that carry earthquake loads
downwards to the foundation (Fig 932)
Fig 932 Reinforced concrete shear walls in
buildings ndash an excellent structural system for
earthquake resistance
Fig 930 Provision of Special confining reinforcement in Footings (IS 13920 1993)
Fig 931 Special Confining Reinforcement Requirement for
Columns under Discontinued Walls (IS 13920 1993)
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Properly designed and detailed buildings with shear walls have shown very good performance in
past earthquakes Shear walls in high seismic regions require special detailing Shear walls are
efficient both in terms of construction cost and effectiveness in minimizing earthquake damage
in structural and non-structural elements (like glass windows and building contents)
Shear walls provide large strength and
stiffness to buildings in the direction of their
orientation which significantly reduces lateral
sway of the building and thereby reduces
damage to structure and its contents
Since shear walls carry large horizontal
earthquake forces the overturning effects on
them are large Thus design of their
foundations requires special attention
Shear walls should be provided along
preferably both length and width However if
they are provided along only one direction a
proper grid of beams and columns in the
vertical plane (called a moment-resistant
frame) must be provided along the other
direction to resist strong earthquake effects
Door or window openings can be provided in shear walls but their size must be small to
ensure least interruption to force flow through walls
Shear walls in buildings must be symmetrically located in plan to reduce ill-effects of twist in
buildings (Fig 933)
Shear walls are more effective when located along exterior perimeter of the building ndash such a
layout increases resistance of the building to twisting
9161 िनय तिजाइन और किरनी दीवारो ो की जयातमति Ductile Design and Geometry of Shear
Walls
Shear walls are oblong in cross-section ie one dimension of the cross-section is much larger
than the other While rectangular cross-section is common L- and U-shaped sections are also
used Overall geometric proportions of the wall types and amount of reinforcement and
connection with remaining elements in the building help in improving the ductility of walls The
Indian Standard Ductile Detailing Code for RC members (IS13920-1993) provides special
design guidelines for ductile detailing of shear walls
917 इमपरवड़ तिजाइन रणनीतियाो Improved design strategies
9171 िातनकारक भको प परभाव स भवनो ो का सोरकषण Protection of Buildings from Damaging
Earthquake Effects
Conventional seismic design attempts to make buildings that do not collapse under strong
earthquake shaking but may sustain damage to non-structural elements (like glass facades) and
to some structural members in the building There are two basic technologies ndashBase Isolation
Fig 933 Shear walls must be symmetric in plan
layout ndash twist in buildings can be avoided
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Devices and Seismic Dampers which are used to protect buildings from damaging earthquake
effects
9172 आधार अलगाव Base Isolation
The idea behind base isolation is to detach (isolate) the building from the ground in such a way
that earthquake motions are not transmitted up through the building or at least greatly reduced
As illustrated in Fig 934 when the ground shakes the rollers freely roll but the building
above does not move Thus no force is
transferred to the building due to shaking of
the ground simply the building does not
experience the earthquake
As illustrated in Fig 935 if the same
building is rested on flexible pads that offer
resistance against lateral movements then
some effect of the ground shaking will be
transferred to the building above
As illustrated in Fig 936 if the flexible
pads are properly chosen the forces induced
by ground shaking can be a few times
smaller than that experienced by the
building built directly on ground namely a
fixed base building
9173 भको पी सोज Seismic Dampers
Seismic dampers are special devices introduced in the building to absorb the energy provided by
the ground motion to the building These dampers act like the hydraulic shock absorbers in cars ndash
much of the sudden jerks are absorbed in the hydraulic fluids and only little is transmitted above
to the chassis of the car
When seismic energy is transmitted through them dampers absorb part of it and thus damp the
motion of the building Commonly used types of seismic dampers (Fig 937) include
Fig 934 Hypothetical Building
Fig 935 Base Isolated Building
Fig 936 Fixed-Base Building
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Viscous dampers ndash Energy is absorbed by
silicone-based fluid passing between piston-
cylinder arrangement
Friction dampers ndash Energy is absorbed by
surfaces with friction between them rubbing
against each other
Yielding dampers ndash Energy is absorbed by
metallic components that yield
In India friction dampers have been provided in an
18-storey RC frame structure in Gurgaon
918 तिजाइन उदािरण Design Example ndash Beam Design of RC Frame with Ductile
Detailing
Exercise ndash 2 Beam Design of RC Frame Building as per Provision of IS 13920 1993 and IS
1893 (Part 1) 2002 Beam marked ABC is considered for Design
Fig 937 Seismic Energy Dissipation Devices
each device is suitable for a certain building
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ELEVATION
Solution
1 General Data Grade of Concrete = M 25
Grade of steel = Fe 415 Tor Steel
2 Load Combinations
As per Cl 63 of IS 1893 (Part 1) 2002 following are load combinations for Earthquake
Loading
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S No Load Combination DL LL EQ Remark
1 15 DL + 15 LL 15 15 ndash As per Table ndash 8
of IS 1893 (Part
1) 2002 2 12 (DL + LL
+ EQx) 15 025 or 050 +12
3 12 (DL + LL ndash EQx) 15 025 or 050 ndash12
4 12 (DL + LL + EQy) 15 025 or 050 +12
5 12 (DL + LL ndash EQy) 15 025 or 050 ndash12
6 15 (DL + EQx) 15 +15
7 15 (DL ndash EQx) 15 ndash15
8 15 (DL + EQy) 15 +15
9 15 (DL ndash EQy) 15 ndash15
10 09 DL + 15 EQx 15 +15
11 09 DL ndash 15 EQx 15 ndash15
12 09 DL + 15 EQy 15 +15
13 09 DL ndash 15 EQy 15 ndash15
EQx implies EQ Loading in X ndash direction amp EQy implies EQ Loading in Y ndash direction
where X amp Y are orthogonal directions and Z is vertical direction These load combinations
are for EQ Loading In practice Wind Load should also be considered in lieu of EQ Load
and critical of the two should be used in the design
In this exercise emphasis is to show calculations for ductile design amp detailing of building
elements subjected to Earthquake in the plan considered Beams parallel to Y ndash direction are
not significantly affected by Earthquake force in X ndash direction (except in case of highly
unsymmetrical building) and vice versa Beams parallel to Y ndash direction are designed for
Earthquake loading in Y ndash direction only
Torsion effect is not considered in this example
3 Force Data
For Beam AB force resultants for various load cases (ie DL LL amp EQ Load) from
Computer Analysis (or manually by any method of analysis) to illustrate the procedure of
design are tabulated below
Table ndash A Force resultants in beam AB for various load cases
Load Case Left End Centre Right End
Shear
(KN)
Moment
(KN-m)
Shear
(KN)
Moment
(KN-m)
Shear
(KN)
Moment
(KN-m)
DL ndash 51 ndash 37 4 32 59 ndash 56
LL ndash 14 ndash 12 1 11 16 ndash 16
EQY 79 209 79 11 79 ndash 119
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Table ndash B Force resultants in beam AB for different load combinations
Load Combinations Left End Centre Right End
Shear
(KN)
Moment
(KN-m)
Shear
(KN)
Moment
(KN-m)
Shear
(KN)
Moment
(KN-m)
15 DL + 15 LL 98 ndash 74 7 64 111 ndash 108
12 (DL + LL + EQy) 31 205 101 52 172 ndash 303
12 (DL + LL ndash EQy) 162 ndash 300 92 31 22 159
15 (DL + EQy) 44 261 127 61 209 ndash 372
15 (DL ndash EQy) 97 ndash 371 115 34 33 205
09 DL + 15 EQy 75 283 124 42 174 ndash 339
09 DL ndash 15 EQy 167 ndash 349 117 15 68 238
4 Various checks for Flexure Member
(i) Check for Axial Stress
As per Cl 611 of IS 13920 1993 flexural axial stress on the member under EQ loading
shall not exceed 01 fck
Factored Axial Force = 000 KN
Factored Axial Stress = 000 MPa lt 010 fck OK
Hence the member is to be designed as Flexure Member
(ii) Check for Member size
As per Cl 613 of IS 13920 1993 width of the member shall not be less than 200 mm
Width of the Beam B = 250 mm gt 200 mm OK
Depth of Beam D = 550 mm
As per Cl 612 member shall have a width to depth ratio of more than 03
BD = 250550 = 04545 gt 03 OK
As per Cl 614 depth of member shall preferably be not more than 14 of the clear span
ie (DL) lt 14 or (LD) gt4
Span = 4 m LD = 4000550 = 727 gt 4 OK
Check for Limiting Longitudinal Reinforcement
Nominal cover to meet Durability requirements as per = 30 mm
Table ndash 16 of IS 4562000 (Cl 2642) for Moderate Exposure
Effective depth for Moderate Exposure conditions = 550 ndash 30 ndash 20 ndash (202)
with 20 mm of bars in two layers = 490 mm
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82
As per Cl 621 (b) of IS 13920 1993 tension steel ratio on any face at any section shall not
be less than = (024 radic fck) fy
= (024 radic25) 415 = 0289 asymp 029
Min Reinforcement = (029100) X 250 X 490 = 356 mm2
Max Reinforcement 25 = (25100) X 250 X 490 = 3063 mm2
(iii) Design for Flexure
Design for Hogging Moment at support A
At end A from Table ndash B Mu = 371 KN-m
Therefore Mu bd2 = 371x10
6 (250 x 490 x 490) = 618
Referring to Table ndash 51 of SP ndash 16 for drsquod = 55490 = 011
We get Ast at top = 2013 Asc = 0866
Therefore Ast at top = (2013100) x 250 x 490
= 2466 mm2
gt 356 mm2 (Min Reinforcement)
lt 3063 mm2 (Max Reinforcement)
Asc at bottom = 0866
As per Cl 623 of IS 13290 1993 positive steel at a joint face must be at least equal to half
the ndashve steel at that face Therefore Asc at bottom must be at least 50 of Ast hence
Revised Asc = 20132 = 10065
Asc at bottom = (10065100) x 250 x 490
= 1233 mm2 gt 426 mm
2 (Min Reinforcement)
lt 3063 mm2 (Max Reinforcement)
Design for Sagging Moment at support A
Mu = 283 KN-m
The beam will be designed as T-beam The limiting capacity of the T-beam assuming xu lt Df
and xu lt xumax may be calculated as follows
Mu = 087 fy Ast d [1- (Ast fy bf d fck)] -------- (Eq ndash 1)
Where Df = Depth of Flange
= 150 mm
xu = Depth of Neutral Axis
xumax = Limiting value of Neutral Axis
= 048 d
= 048 X 490
= 23520 mm
bw = 250 mm
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83
bf = Width of Flange
= (L06) + bw + 6 Df or cc of beam
= (07 X 40006) + 250 + 6 X 150
= 467 + 250 + 900 = 1617 mm or 4000 mm cc
[Lower of two is to be adopted]
Substituting the values in Eq ndash 1 and solving the quadratic equation
283 X 106 = 087 X 415 Ast X 490 [1ndash (Ast X 415) (1617 X 490 X 25)]
= 1769145 Ast [1 ndash 2095 X 10-5
Ast]
283 X 106 = 1769145 Ast ndash 3706 Ast
2]
3706 Ast2 ndash 1769145 Ast + 283 X 10
6 = 0
Ast = [1769145 plusmn radic(17691452 ndash 4 X 3706 X 283 X 10
6)] 2 X 3706
= [1769145 plusmn radic(3129874 X 1010
ndash 4195192 X 106)] 2 X 3706
= (1769145 plusmn 16463155) 7412
Ast at bottom = 165717 mm2 gt 35600 mm
2
lt 306300 mm2 OK
It is necessary to check the design assumptions before finalizing the reinforcement
xu = (087 fy Ast) (036 fck bf)
= (087 X 415 X 1657) (036 X 25 X 1617)
= 4110 mm lt 150 mm OK
lt df
lt xumax = 048 X 490 = 235 mm OK
Ast = [1657(250X490)] X 100 = 1353
As per Cl 624 ldquoSteel provided at each of the top amp bottom face of the member at any one
section along its length shall be at least equal to 14th
of the maximum (-ve) moment steel
provided at the face of either joint
For Centre Mu = 64 KN-m
64 X 106 = 087 X 415 Ast X 490 [1ndash (Ast X 415) (1617 X 490 X 25)]
= 1769145 Ast [1 ndash 2095 X 10-5
Ast]
64 X 106 = 1769145 Ast ndash 3706 Ast
2]
3706 Ast2 ndash 1769145 Ast + 64 X 10
6 = 0
Ast = [1769145 plusmn radic(17691452 ndash 4 X 3706 X 64 X 10
6)] 2 X 3706
= 365 mm2
For Right Support Mu = 238 KN-m
238 X 106 = 087 X 415 Ast X 490 [1ndash (Ast X 415) (1617 X 490 X 25)]
= 1769145 Ast [1 ndash 2095 X 10-5
Ast]
238 X 106 = 1769145 Ast ndash 3706 Ast
2]
3706 Ast2 ndash 1769145 Ast + 238 X 10
6 = 0
Ast = [1769145 plusmn radic(17691452 ndash 4 X 3706 X 238 X 10
6)] 2 X 3706
= 1386 mm2
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(iv) Reinforcement Requirement
Top reinforcement is larger of Ast at top for hogging moment or Asc at top for sagging
moment ie 2466 mm2 or 968 mm
2 Hence provide 2466 mm
2 at top
Bottom reinforcement is larger of Asc at bottom for hogging moment or Ast at bottom for
sagging moment ie 1233 mm2 or 1936 mm
2 Hence provide 1936 mm
2 at bottom
Details of Reinforcement
Top Reinforcement
Beam AB Left End Centre Right End
Hogging Moment ndash 371 - ndash 371
Mu bd2 618 - 618
Ast at top 2013 - 2013
Asc at bottom 0866 lt 2013 2 =
10065 Hence
revised Asc = 10065
- 0866
Revised to
10065 as per Cl
623 of IS
139201993
Bottom Reinforcement
Sagging Moment 283 64 238
Ast at bottom Ast req = 1657 mm2
= 1353
gt 20132 =
10065 OK
Provide Ast at bottom
= 1353
Ast req = 365 mm2
= 0298
gt 029
gt 20134 =
0504 OK
As per Cl 624 of IS
139201993
Provide Ast at bottom
= 0504
Ast req = 1386 mm2
= 117
gt 029
gt 20132 =
10065
Provide Ast at
bottom = 117
Asc at top Asc req = 1657 2
= 829 mm2
= 0677
gt 029
gt 2013 4 =
0504 OK
Asc req = 05042
= 0252
gt 029 Provide MinAsc = 029
Asc req = 1657 2
= 829 mm2
= 0677
gt 029
gt 2013 4
= 0504
OK
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Summary of Reinforcement required
Beam Left End Centre Right End
Top = 2013
= 2466 mm2
Bottom = 1353
= 1658 mm2
Top = 0504
= 618 mm2
Bottom = 0504
= 618 mm2
Top = 2013
= 2466 mm2
Bottom = 10065
= 1233 mm2
Reinforcement provided
2 ndash 20Φ cont + 4 ndash 25Φ extra
Ast = 2592 mm2 (2116)
2 ndash 20Φ cont + 2 ndash 20Φ extra
+ 2 ndash 16 Φ
Ast = 1658 mm2 (1353)
2 ndash 20Φ cont
Ast = 628 mm2 (0512)
2 ndash 20Φ cont
Ast = 628 mm2 (0512)
2 ndash 20Φ cont
+ 4 ndash 25Φ extra
Top = 2592 mm2
2 ndash 20Φ cont
+ 2 ndash 20Φ extra + 2 ndash 16Φ
Ast = 1658 mm2 (1353)
Details of Reinforcement
Ld = Development Length in tension
db = Dia of bar
For Fe 415 steel and M25 grade concrete as per Table ndash 65 of SP ndash 16
For 25Φ bars 1007 + 10Φ - 8Φ = 1007+50 = 1057 mm
For 20Φ bars 806 + 2Φ = 806+40 = 846 mm
(v) Design for Shear
Tensile steel provided at Left End = 2116
Permissible Design Stress of Concrete
(As per Table ndash 19 of IS 4562000) τc = 0835 MPa
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Design Shear Strength of Concrete = τc b d
= (0835 X 250 X 490) 1000
= 102 KN
Similarly Design Shear Strength of Concrete at centre for Ast = 0512
τc = 0493 MPa
Shear Strength of Concrete at centre = τc b d
= (0493 X 250 X 490) 1000
= 6040 KN
(vi) Shear force due to Plastic Hinge Formation at the ends of the beam
The additional shear due to formation of plastic hinges at both ends of the beams is evaluated
as per Cl 633 of IS 139201993 is given by
Vsway to right = plusmn 14 [MulimAs
+ MulimBh
] L
Vsway to left = plusmn 14 [MulimAh
+ MulimBs
] L
Where
MulimAs
= Sagging Ultimate Moment of Resistance of Beam Section at End A
MulimAh
= Hogging Ultimate Moment of Resistance of Beam Section at End A
MulimBh
= Sagging Ultimate Moment of Resistance of Beam Section at End B
MulimBs
= Hogging Ultimate Moment of Resistance of Beam Section at End B
At Ends beam is provided with steel ndash pt = 2116 pc = 1058
Referring Table 51 of SP ndash 16 for pt = 2116 pc = 1058
The lowest value of MuAh
bd2 is found
MuAh
bd2 = 645
Hogging Moment Capacity at End A
MuAh
= 645 X 250 X 4902
= 38716 X 108 N-mm
= 38716 KN-m
Similarly for MuAs
pt = 1058 pc = 2116
Contribution of Compressive steel is ignored while calculating the Sagging Moment
Capacity at T-beam
MuAs
= 087 fy Ast d [1- (Ast fy bf d fck)]
= 087 X 415 X 1658 X 490 [1ndash (1658 X 415 1617 X 490 X 25)]
= 28313 KN-m
Similarly for Right End of beam
MuBh
= 38716 KN-m amp MuBs
= 28313 KN-m
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Shear due to Plastic Hinge is calculated as
Vsway to right = plusmn 14 [MuAs
+ MuBh
] L
= plusmn 14 [28313 + 38716] 4
= 23460 KN
Vsway to left = plusmn 14 [MuAh
+ MuBs
] L
= plusmn 14 [38716 + 28313] 4
= 23460 KN
Design Shear
Dead Load of Slab = 50 KNm2 Live Load = 40 KNm
2
Load due to Slab in Beam AB = 2 X [12 X 4 X 2] X 5 = 40 KN (10 KNm)
Self Wt Of Beam = 025 X 055 X 25 X 4 = 1375 KN (344 KNm)
asymp 1400 KN
Live Load = 2 X [12 X 4 X 2] X 4 = 32 KN (8 KNm)
Shear Force due to DL = 12 X [40 + 14] = 27 KN
Shear Force due to LL = 12 X [32] = 16 KN
As per Cl 633 of IS 139201993 the Design shear at End A ie Vua and Design Shear at
End B ie Vub are computed as
(i) For Sway Right
Vua = VaD+L
ndash 14 [MulimAs
+ MulimBh
] LAB
Vub = VbD+L
+ 14 [MulimAs
+ MulimBh
] LAB
(ii) For Sway Left
Vua = VaD+L
+ 14 [MulimAh
+ MulimBs
] LAB
Vub = VbD+L
ndash 14 [MulimAh
+ MulimBs
] LAB
Where
VaD+L
amp VbD+L
= Shear at ends A amp B respectively due to vertical load with
Partial Safety Factor of 12 on Loads
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VaD+L
= VbD+L
= 12 (D+L) 2
--------------For equ (i)
---------------For equ (ii)
14 X [MuAs
+ MuBh
] L = 23460 KN
14 X [MuAh
+ MuBs
] L = 23460 KN
VaD = Vb
D = 12 X 27 = 324
= 516
VaL = Vb
L = 12 X 16 = 192
Vua = [12 (27+16)] ndash 23460 = 516 ndash 23460 = (-) 18300 KN
Vub = [12 (27+16)] + 23460 = 516 + 23460 = (+) 28620 KN
Vub = [12 (27+16)] + 23460 = 516 + 23460 = (+) 28620 KN
Vua = [12 (27+16)] ndash 23460 = 516 ndash 23460 = (-) 18300 KN
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As per Cl 633 of IS 139201993 the Design Shear Force to be resisted shall be of
maximum of
(i) Calculate factored SF as per analysis ( Refer Table ndash B)
(ii) Shear Force due to formation of Plastic Hinges at both ends of the beam plus
factored gravity load on the span
Hence Design shear Force Vu will be 28620 KN (corresponding to formation of Plastic
Hinge)
From Analysis as per Table ndash B SF at mid-span of the beam is 127 KN However Shear
due to formation of Plastic Hinge is 23460 KN Hence design shear at centre of span is
taken as 23460 KN
The required capacity of shear reinforcement at ends
Vus = Vu - Vc
= 28620 ndash 102
= 18420 KN
And at centre Vus = 23460 ndash 6040
= 17420 KN
At supports
Vus d = 28620 49 = 584 KNcm
Therefore requirement of stirrups is
12Φ ndash 2 legged strippus 135 cc [Vus d = 606]
However provide 12Φ ndash 2 legged strippus 120 cc as per provision of Cl 635 of IS
139201993 [Vus d = 6806]
At centre
Vus d = 23460 49 = 478 KNcm
Provide 12Φ ndash 2 legged strippus 170 cc [Vus d = 4804]
As per Cl 635 of IS 139201993 the spacing of stirrups in the mid-span should not
exceed d2 = 4902 = 245 mm
Minimum Shear Reinforcement as per Cl 26516 of IS 4562000 is
Sv = Asv X 08 fy 046
= (2 X 79 X 087 X 415) (250 X 04)
= 570 mm
As per CL 635 of IS 139201993 ldquoSpacing of Links over a length of 2d at either end of
beam shall not exceed
(i) d4 = 4904 = 12250 mm
(ii) 8 times dia of smallest longitudinal bar = 8 X 16 = 128 mm
However it need not be less than 100 mm
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The reinforcement detailing is shown as below
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अधयाय Chapter ndash 10
अलप सामरथय तचनाई सोरचनाओो क तनमायण Construction of Low Strength Masonry Structures
Two types of construction are included herein namely
a) Brick construction using weak mortar and
b) Random rubble and half-dressed stone masonry construction using different mortars such as
clay mud lime-sand and cement sand
101 भको प क दौरान ईोट तचनाई की दीवारो ो का वयविार Behaviour of Brick Masonry Walls
during Earthquakes
Of the three components of a masonry building (roof wall and foundation as illustrated in
Fig101) the walls are most vulnerable to damage caused by horizontal forces due to earthquake
Ground vibrations during earthquakes cause inertia forces at locations of mass in the building (Fig 102) These forces travel through the roof and walls to the foundation The main emphasis
is on ensuring that these forces reach the ground without causing major damage or collapse
A wall topples down easily if pushed
horizontally at the top in a direction
perpendicular to its plane (termed weak
Fig 101 Basic components of Masonry Building
Fig 103 For the direction of Earthquake shaking
shown wall B tends to fail
at its base
Fig 102 Effect of Inertia in a building when shaken
at its base
Fig 104 Direction of force on a wall critically determines
its earthquake performance
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direction) but offers much greater resistance if pushed along its length (termed strong direction) (Fig 103 amp 104)
The ground shakes simultaneously in the vertical and two horizontal directions during
earthquakes However the horizontal vibrations are the most damaging to normal masonry
buildings Horizontal inertia force developed at the
roof transfers to the walls acting either in the weak
or in the strong direction If all the walls are not tied
together like a box the walls loaded in their weak
direction tend to topple
To ensure good seismic performance all walls must
be joined properly to the adjacent walls In this way
walls loaded in their weak direction can take
advantage of the good lateral resistance offered by
walls loaded in their strong direction (Fig 105)
Further walls also need to be tied to the roof and
foundation to preserve their overall integrity
102 तचनाई वाली इमारिो ो म बॉकस एकशन कस सतनतिि कर How to ensure Box Action in
Masonry Buildings
A simple way of making these walls behave well during earthquake shaking is by making them
act together as a box along with the roof at the top and with the foundation at the bottom A
number of construction aspects are required to ensure this box action
Firstly connections between the walls should be good This can be achieved by (a) ensuring
good interlocking of the masonry courses at the junctions and (b) employing horizontal bands
at various levels particularly at the lintel level
Secondly the sizes of door and window
openings need to be kept small The smaller
the opening the larger is the resistance
offered by the wall
Thirdly the tendency of a wall to topple
when pushed in the weak direction can be
reduced by limiting its length-to-thickness
and height to-thickness ratios Design codes
specify limits for these ratios A wall that is
too tall or too long in comparison to its
thickness is particularly vulnerable to
shaking in its weak direction (Fig 106)
Fig 106 Slender walls are vulnerable
Fig 105 Wall B properly connected to Wall A
(Note roof is not shown) Walls A
(loaded in strong direction) support
Walls B (loaded in weak direction)
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Brick masonry buildings have large mass and hence attract large horizontal forces during
earthquake shaking They develop numerous cracks under both compressive and tensile forces
caused by earthquake shaking The focus of earthquake resistant masonry building construction
is to ensure that these effects are sustained without major damage or collapse Appropriate choice
of structural configuration can help achieve this
The structural configuration of masonry buildings
includes aspects like (a) overall shape and size of the
building and (b) distribution of mass and
(horizontal) lateral load resisting elements across the
building
Large tall long and un-symmetric buildings perform
poorly during earthquakes A strategy used in making
them earthquake resistant is developing good box
action between all the elements of the building ie
between roof walls and foundation (Fig 107) For
example a horizontal band introduced at the lintel
level ties the walls together and helps to make them
behave as a single unit
103 कषतिज बि की भतमका Role of Horizontal Bands
Horizontal bands are the most important
earthquake-resistant feature in masonry
buildings The bands are provided to hold a
masonry building as a single unit by tying all
the walls together and are similar to a closed
belt provided around cardboard boxes
(Fig 108 amp 109)
The lintel band undergoes bending and pulling actions during earthquake shaking
(Fig1010)
To resist these actions the construction of lintel band requires special attention
Fig 107 Essential requirements to ensure
box action in a masonry building
Fig 108 Building with flat roof
Fig 109 Two-storey Building with pitched roof
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Bands can be made of wood (including bamboo splits) or of reinforced concrete (RC) the
RC bands are the best (Fig 1011)
The straight lengths of the band must be properly connected at the wall corners
In wooden bands proper nailing of straight lengths with spacers is important
In RC bands adequate anchoring of steel links with steel bars is necessary
The lintel band is the most important of all and needs to be provided in almost all buildings
The gable band is employed only in buildings with pitched or sloped roofs
In buildings with flat reinforced concrete or reinforced brick roofs the roof band is not
required because the roof slab also plays the role of a band However in buildings with flat
timber or CGI sheet roof roof band needs to be provided In buildings with pitched or sloped
roof the roof band is very important
Plinth bands are primarily used when there is concern about uneven settlement of foundation
soil
Lintel band Lintel band is a band provided at lintel level on all load bearing internal external
longitudinal and cross walls
Roof band Roof band is a band provided immediately below the roof or floors Such a band
need not be provided underneath reinforced concrete or brick-work slabs resting on bearing
Fig 1010 Bending and pulling in lintel bands ndash Bands must be capable of resisting these actions
Fig 1011 Horizontal Bands in masonry buildings ndash RC bands are the best
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walls provided that the slabs are continuous over the intermediate wall up to the crumple
sections if any and cover the width of end walls fully or at least 34 of the wall thickness
Gable band Gable band is a band provided at the top of gable masonry below the purlins This
band shall be made continuous with the roof band at the eaves level
Plinth band Plinth band is a band provided at plinth level of walls on top of the foundation
wall This is to be provided where strip footings of masonry (other than reinforced concrete or
reinforced masonry) are used and the soil is either soft or uneven in its properties as frequently
happens in hill tracts This band will serve as damp proof course as well
104 अधोलोब सदढीकरण Vertical Reinforcement
Vertical steel at corners and junctions of walls which are up to 340 mm (1frac12 brick) thick shall be
provided as specified in Table 101 For walls thicker than 340 mm the area of the bars shall be
proportionately increased
No vertical steel need be provided in category A building The vertical reinforcement shall be
properly embedded in the plinth masonry of foundations and roof slab or roof band so as to
develop its tensile strength in bond It shall be passing through the lintel bands and floor slabs or
floor level bands in all storeys
Table ndash 101 Vertical Steel Reinforcement in Masonry Walls with Rectangular Masonry Units (IS 4326 1993)
No of Storeys Storey Diameter of HSD Single Bar in mm at Each Critical Section
Category B Category C Category D Category E One mdash Nil Nil 10 12
Two Top
Bottom
Nil
Nil
Nil
Nil
10
12
12
16
Three Top
Middle
Bottom
Nil
Nil
Nil
10
10
12
10
12
12
12
16
16
Four Top
Third
Second
Bottom
10
10
10
12
10
10
12
12
10
12
16
20
Four storeyed
building not
permitted
NOTES
1 The diameters given above are for HSD bars For mild-steel plain bars use equivalent diameters as given under
Table ndash 106 Note 2
2 The vertical bars will be covered with concrete M15 or mortar 1 3 grade in suitably created pockets around the
bars This will ensure their safety from corrosion and good bond with masonry
3 In case of floorsroofs with small precast components also refer 923 of IS 4326 1993 for floorroof band details
Bars in different storeys may be welded (IS 2751 1979 and IS 9417 1989 as relevant) or
suitably lapped
Vertical reinforcement at jambs of window and door openings shall be provided as per
Table ndash 101 It may start from foundation of floor and terminate in lintel band (Fig 1017)
Typical details of providing vertical steel in brickwork masonry with rectangular solid units
at corners and T-junctions are shown in Fig 1012
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105 दीवारो ो म सराखो ो का सोरकषण Protection of Openings in Walls
Horizontal bands including plinth band lintel band and roof band are provided in masonry
buildings to improve their earthquake performance Even if horizontal bands are provided
masonry buildings are weakened by the openings in their walls
Embedding vertical reinforcement bars in the edges of the wall piers and anchoring them in the
foundation at the bottom and in the roof band at the top forces the slender masonry piers to
undergo bending instead of rocking In wider wall piers the vertical bars enhance their capability
to resist horizontal earthquake forces and delay the X-cracking Adequate cross-sectional area of
these vertical bars prevents the bar from yielding in tension Further the vertical bars also help
protect the wall from sliding as well as from collapsing in the weak direction
However the most common damage observed after an earthquake is diagonal X-cracking of
wall piers and also inclined cracks at the corners of door and window openings
When a wall with an opening deforms during earthquake shaking the shape of the opening
distorts and becomes more like a rhombus - two opposite corners move away and the other two
come closer Under this type of deformation the corners that come closer develop cracks The
cracks are bigger when the opening sizes are larger Steel bars provided in the wall masonry all
Fig 1012 Typical Details of Providing Vertical Steel Bars in Brick Masonry (IS 4326 1993)
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around the openings restrict these cracks at the corners In summary lintel and sill bands above
and below openings and vertical reinforcement adjacent to vertical edges provide protection
against this type of damage (Fig 1013)
106 भको प परतिरोधी ईोट तचनाई भवन क तनमायण िि सामानय तसदाोि General Principles for
Construction of Earthquake Resistant Brick Masonry Building
Low Strength Masonry constructions should not be permitted for important buildings
It will be useful to provide damp-proof course at plinth level to stop the rise of pore water
into the superstructure
Precautions should be taken to keep the rain water away from soaking into the wall so that
the mortar is not softened due to wetness An effective way is to take out roof projections
beyond the walls by about 500 mm
Use of a water-proof plaster on outside face of walls will enhance the life of the building and
maintain its strength at the time of earthquake as well
Ignoring tensile strength free standing walls should be checked against overturning under the
action of design seismic coefficient ah allowing for a factor of safety of 15
1061 भवनो ो की शरतणयाा Categories of Buildings
For the purpose of specifying the earthquake resistant features in masonry and wooden buildings
the buildings have been categorized in five categories A to E based on the seismic zone and the
importance of building I
Where
I = importance factor applicable to the
building [Ref Clause 642 and
Table - 6 of IS 1893 (Part 1) 2002]
The building categories are given in
Table ndash 102
Fig 1013 Cracks at corners of openings in a masonry building ndash reinforcement around them helps
Table -102 Building Categories for Earthquake Resisting Features (IS 4326 1993)
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1062 कमजोर गार म ईोट तचनाई कायय Brickwork in Weak Mortars
The fired bricks should have a compressive strength not less than 35 MPa Strength of bricks
and wall thickness should he selected for the total building height
The mortar should be lime-sand (13) or clay mud of good quality Where horizontal steel is
used between courses cement-sand mortar (13) should be used with thickness so as to cover
the steel with 6 mm mortar above and below it Where vertical steel is used the surrounding
brickwork of 1 X 1 or lfrac12 X 1frac12 brick size depending on wall thickness should preferably be
built using 16 cement-sand mortar
The minimum wall thickness shall be one brick in one storey construction and one brick in
top storey and 1frac12brick in bottom storeys of up to three storey constructions It should also
not be less than l16 of the length of wall between two consecutive perpendicular walls
The height of the building shall be restricted to the following where each storey height shall
not exceed 30 m
For Categories A B and C - three storeys with flat roof and two storeys plus attic pitched
roof
For Category D - two storeys with flat roof and one storey plus attic for pitched roof
1063 आयिाकार तचनाई इकाइयो ो वाला तचनाई तनमायण Masonry Construction with
Rectangular Masonry Units
General requirements for construction of masonry walls using rectangular masonry units are
10631 तचनाई इकाइयाो Masonry Units
Well burnt bricks conforming to IS 1077 1992 or solid concrete blocks conforming to IS
2185 (Part 1) 1979 and having a crushing strength not less than 35 MPa shall be used The
strength of masonry unit required
shall depend on the number of storeys
and thickness of walls
Squared stone masonry stone block
masonry or hollow concrete block
masonry as specified in IS 1597 (Part
2) 1992 of adequate strength may
also be used
10632 गारा Mortar
Mortars such as those given in Table
ndash 103 or of equivalent specification
shall preferably be used for masonry
Table ndash 103 Recommended Mortar Mixes (IS 4326 1993)
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construction for various categories of buildings
Where steel reinforcing bars are provided in masonry the bars shall be embedded with
adequate cover in cement sand mortar not leaner than 13 (minimum clear cover 10 mm) or in
cement concrete of grade M15 (minimum clear cover 15 mm or bar diameter whichever
more) so as to achieve good bond and corrosion resistance
1064 दीवार Walls
Masonry bearing walls built in mortar as specified in 10632 above unless rationally
designed as reinforced masonry shall not be built of greater height than 15 m subject to a
maximum of four storeys when measured from the mean ground level to the roof slab or
ridge level
The bearing walls in both directions shall be straight and symmetrical in plan as far as
possible
The wall panels formed between cross walls and floors or roof shall be checked for their
strength in bending as a plate or as a vertical strip subjected to the earthquake force acting on
its own mass
Note mdash For panel walls of 200 mm or larger thickness having a storey height not more than
35 metres and laterally supported at the top this check need not be exercised
1065 तचनाई बॉणड Masonry Bond
For achieving full strength of
masonry the usual bonds
specified for masonry should be
followed so that the vertical joints
are broken properly from course
to course To obtain full bond
between perpendicular walls it is
necessary to make a slopping
(stepped) joint by making the
corners first to a height of 600
mm and then building the wall in
between them Otherwise the
toothed joint (as shown in Fig
1014) should be made in both the
walls alternatively in lifts of
about 450 mm
Panel or filler walls in framed buildings shall be properly bonded to surrounding framing
members by means of suitable mortar (as given in 10632 above) or connected through
dowels
Fig 1014 Alternating Toothed Joints in Walls at Corner and T-Junction (IS 4326 1993)
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107 ओपतनोग का परभाव Influence of Openings
Openings are functional necessities in buildings
During earthquake shaking inertia forces act in
the strong direction of some walls and in the weak
direction of others Walls shaken in the weak
direction seek support from the other walls ie
walls B1 and B2 seek support from walls A1 and
A2 for shaking in the direction To be more
specific wall B1 pulls walls A1 and A2 while
wall B2 pushes against them
Thus walls transfer loads to each other at their
junctions (and through the lintel bands and roof)
Hence the masonry courses from the walls
meeting at corners must have good interlocking
(Fig 1015) For this reason openings near the
wall corners are detrimental to good seismic
performance Openings too close to wall corners
hamper the flow of forces from one wall to
another Further large openings weaken walls
from carrying the inertia forces in their own
plane Thus it is best to keep all openings as small as possible and as far away from the corners
as possible
108 धारक दीवारो ो म ओपतनोग परदाि करि की सामानय आवशयकताए General Requirements of
Providing Openings in Bearing Walls
Door and window openings in walls reduce their lateral load resistance and hence should
preferably be small and more centrally located The guidelines on the size and position of
opening are given in Table ndash 104 and in Fig 1016
Fig 1015 Regions of force transfer from weak
walls to strong walls in a masonry building ndash Wall
B1 pulls walls A1 and A2 while wall B2pushes walls
A1 and A2
Fig 1016 Dimensions of Openings and Piers for
Recommendations in Table 3 (IS 4326 1993)
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Table ndash 104 Size and Position of Openings in Bearing Walls
S
No
Position of opening Details of Opening for Building Category
A and B C D and E
1 Distance b5 from the inside corner of outside wall Min Zero mm 230 mm 450 mm
2 For total length of openings the ratio (b1+b2+b3)l1 or
(b6+b7)l2 shall not exceed
a) one-storeyed building
b) two-storeyed building
c) 3 or 4-storeyed building
060
050
042
055
046
037
050
042
033
3 Pier width between consecutive openings b4 Min 340 mm 450 mm 560 mm
4 Vertical distance between two openings one above the
other h3 Min
600 mm 600 mm 600 mm
5 Width of opening of ventilator b8 Max 900 mm 900 mm 900 mm
Openings in any storey shall preferably have their top at the same level so that a continuous
band could be provided over them including the lintels throughout the building
Where openings do not comply with the guidelines as given in Table ndash 104 they should be
strengthened by providing reinforced concrete or reinforcing the brickwork as shown in Fig
1017 with high strength deformed (HSD) bars of 8 mm dia but the quantity of steel shall be
increased at the jambs
If a window or ventilator is to be
projected out the projection shall be in
reinforced masonry or concrete and well
anchored
If an opening is tall from bottom to
almost top of a storey thus dividing the
wall into two portions these portions
shall be reinforced with horizontal
reinforcement of 6 mm diameter bars at
not more than 450 mm intervals one on
inner and one on outer face properly tied
to vertical steel at jambs corners or
junction of walls where used
The use of arches to span over the
openings is a source of weakness and
shall be avoided Otherwise steel ties
should be provided
109 भको पी सदढ़ीकरण वयवसथा Seismic Strengthening Arrangements
All masonry buildings shall be strengthened as specified for various categories of buildings as
listed in Table ndash 105
Fig 1017 Strengthening Masonry around Opening (IS
4326 1993)
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Table ndash 105 Strengthening Arrangements Recommended for Masonry Buildings
(Rectangular Masonry Units)(IS 4326 1993)
Building Category Number of Storeyes Strengthening to be Provided in all Storeys
A
i) 1 to 3
ii) 4
a
a b c
B
i) 1 to 3
ii) 4
a b c f g
a b c d f g
C
i) 1 and 2
ii) 3 and 4
a b c f g
a to g
D
i) 1 and 2
ii) 3 and 4
a to g
a to h
E 1 to 3 a to h
Where
a mdash Masonry mortar
b mdash Lintel band
c mdash Roof band and gable band where necessary
d mdash Vertical steel at corners and junctions of walls
e mdash Vertical steel at jambs of openings
f mdash Bracing in plan at tie level of roofs
g mdash Plinth band where necessary and
h mdash Dowel bars
4th storey not allowed in category E
NOTE mdash In case of four storey buildings of category B the requirements of vertical steel may be checked
through a seismic analysis using a design seismic coefficient equal to four times the one given in (a) 3423
of IS 1893 1984 (This is because the brittle behaviour of masonry in the absence of vertical steel results in
much higher effective seismic force than that envisaged in the seismic coefficient provided in the code) If
this analysis shows that vertical steel is not required the designer may take the decision accordingly
The overall strengthening arrangements to be adopted for category D and E buildings which
consist of horizontal bands of reinforcement at critical levels vertical reinforcing bars at corners
junctions of walls and jambs of opening are shown in Fig 1018 amp 1019
Fig 1018 Overall Arrangement of Reinforcing Fig 1019 Overall Arrangement of Reinforcing Masonry
Masonry Buildings (IS 4326 1993) Building having Pitched Roof (IS 4326 1993)
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103
1091 पटट का अनभाग एवो सदढीकरण Section and Reinforcement of Band
The band shall be made of reinforced concrete of grade not leaner than M15 or reinforced
brickwork in cement mortar not leaner than 13 The bands shall be of the full width of the wall
not less than 75 mm in depth and reinforced with steel as indicated in Table ndash 106
Table ndash 106 Recommended Longitudinal Steel in Reinforced Concrete Bands (IS 4326 1993)
Span Building Category
B
Building Category
C
Building Category
D
Building Category
E No of Bars Dia No of Bars Dia No of Bars Dia No of Bars Dia
(1) (2) (3) (4) (5) (6) (7) (8) (9)
m mm mm mm mm
5 or less 2 8 2 8 2 8 2 10
6 2 8 2 8 2 10 2 12
7 2 8 2 10 2 12 4 10
8 2 10 2 12 4 10 4 12
Notes -
1 Span of wall will be the distance between centre lines of its cross walls or buttresses For spans greater than 8 m
it will be desirable to insert pillasters or buttresses to reduce the span or special calculations shall be made to
determine the strength of wall and section of band
2 The number and diameter of bars given above pertain to high strength deformed bars If plain mild-steel bars are
used keeping the same number the following diameters may be used
High Strength Def Bar dia 8 10 12 16 20
Mild Steel Plain bar dia 10 12 16 20 25
3 Width of RC band is assumed same as the thickness of the wall Wall thickness shall be 200 mm minimum A
clear cover of 20 mm from face of wall will be maintained
4 The vertical thickness of RC band be kept 75 mm minimum where two longitudinal bars are specified one on
each face and 150 mm where four bars are specified
5 Concrete mix shall be of grade M15 of IS 456 1978 or 1 2 4 by volume
6 The longitudinal steel bars shall be held in position by steel links or stirrups 6 mm dia spaced at 150 mm apart
NOTE mdash In coastal areas the concrete grade shall be M20 concrete and the filling mortar of 13
(cement-sand with water proofing admixture)
As illustrated in Fig 1020 ndash
In case of reinforced brickwork the
thickness of joints containing steel bars shall
be increased so as to have a minimum
mortar cover of 10 mm around the bar In
bands of reinforced brickwork the area of
steel provided should be equal to that
specified above for reinforced concrete
bands
In category D and E buildings to further
iterate the box action of walls steel dowel
bars may be used at corners and T-junctions
of walls at the sill level of windows to
length of 900 mm from the inside corner in
each wall Such dowel may be in the form of
Fig 1020 Reinforcement and Bending Detail in RC Band ((IS 4326 1993)
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104
U stirrups 8 mm dia Where used such bars must be laid in 13 cement-sand-mortar with a
minimum cover of 10 mm on all sides to minimize corrosion
1010 भको प क दौरान सटोन तचनाई की दीवारो ो का वयविार Behaviour of Stone Masonry
Walls during Earthquakes
Stone has been used in building construction in India since ancient times since it is durable and
locally available The buildings made of thick stone masonry walls (thickness ranges from 600 to
1200 mm) are one of the most deficient building systems from earthquake-resistance point of
view
The main deficiencies include excessive wall thickness absence of any connection between the
two wythes of the wall and use of round stones (instead of shaped ones) (Fig 1021 amp 1022)
Note A wythe is a continuous vertical section of masonry one unit in thickness A wythe may be
independent of or interlocked with the adjoining wythe (s) A single wythe of brick that is not
structural in nature is referred to as a veneer (httpsenwikipediaorgwikiWythe)
The main patterns of earthquake damage include
(a) bulging separation of walls in the horizontal direction into two distinct wythes
(b) separation of walls at corners and T-junctions
(c) separation of poorly constructed roof from walls and eventual collapse of roof and
(d) disintegration of walls and eventual collapse of the whole dwelling
In the 1993 Killari (Maharashtra) earthquake alone over 8000 people died most of them buried
under the rubble of traditional stone masonry dwellings Likewise a majority of the over 13800
deaths during 2001 Bhuj (Gujarat) earthquake is attributed to the collapse of this type of
construction
1011 भको प परतिरोधी सटोन तचनाई भवन क तनमायण िि सामानय तसदाोि General principle for
construction of Earthquake Resistant stone masonry building
10111 भको प परतिरोधी लकषण Earthquake Resistant Features
1 Low strength stone masonry buildings are weak against earthquakes and should be avoided
in high seismic zones Inclusion of special earthquake-resistant features may enhance the
earthquake resistance of these buildings and reduce the loss of life These features include
Fig 1021 Separation of a thick wall into two layers Fig 1022 Separation of unconnected adjacent walls at junction
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105
(a) Ensure proper wall construction
(b) Ensure proper bond in masonry courses
(c) Provide horizontal reinforcing elements
(d) Control on overall dimensions and heights
2 The mortar should be cement-sand (1 6) lime-sand (1 3) or clay mud of good quality
3 The wall thickness should not be larger than 450
mm Preferably it should be about 350 mm and
the stones on the inner and outer wythes should be
interlocked with each other
NOTE - If the two wythes are not interlocked they
tend to delaminate during ground shaking bulge
apart (as shown in Fig 1023) and buckle
separately under vertical load leading to
complete collapse of the wall and the building
4 The masonry should preferably be brought to courses at not more than 600 mm lift
5 lsquoThroughrsquo stones at full length
equal to wall thickness should be
used in every 600 mm lift at not
more than 12 m apart
horizontally If full length stones
are not available stones in pairs
each of about 34 of the wall
thickness may be used in place of
one full length stone so as to
provide an overlap between them
(as shown in Fig 1024)
6 In place of lsquothroughrsquo stones lsquobonding elementsrsquo of steel bars 8 to 10 mm dia bent to S-shape
or as hooked links may be used with a cover of 25 mm from each face of the wall (as shown
in Fig 1024) Alternatively wood-bars of 38 mm X 38 mm cross section or concrete bars of
50 mm X50 mm section with an 8 mm dia rod placed centrally may be used in place of
throughrsquo stones The wood should be well treated with preservative so that it is durable
against weathering and insect action
7 Use of lsquobondingrsquo elements of adequate length should also be made at corners and junctions of
walls to break the vertical joints and provide bonding between perpendicular walls
8 Height of the stone masonry walls (random rubble or half-dressed) should be restricted as
follows with storey height to be kept 30 m maximum and span of walls between cross walls
to be limited to 50 m
Fig 1023 Wall delaminated with buckled
withes (IS 13828 1993)
Fig 1024 Through Stone and Bond Elements (IS 13828 1993)
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a) For categories A and B ndash Two storeys with flat roof or one storey plus attic if walls are
built in lime-sand or mud mortar and -one storey higher if walls are built in cement-sand
1 6 mortar
b) For categories C and D - Two storeys with flat roof or two storeys plus attic for pitched
roof if walls are built in 1 6 cement mortar and one storey with flat roof or one storey
plus attic if walls are built in lime-sand or mud mortar respectively
9 If walls longer than 5 m are needed buttresses may be used at intermediate points not farther
apart than 40 m The size of the buttress be kept of uniform thickness Top width should be
equal to the thickness of main wall t and the base width equal to one sixth of wall height
10 The stone masonry dwellings must have horizontal bands (plinth lintel roof and gable
bands) These bands can be constructed out of wood or reinforced concrete and chosen based
on economy It is important to provide at least one band (either lintel band or roof band) in
stone masonry construction
Note Although this type of stone masonry construction practice is deficient with regards to earthquake
resistance its extensive use is likely to continue due to tradition and low cost But to protect human lives
and property in future earthquakes it is necessary to follow proper stone masonry construction in seismic
zones III and higher Also the use of seismic bands is highly recommended
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107
अधयाय Chapter- 11
भकपीय रलयमकन और रटरोफिट ग
SEISMIC EVALUATION AND RETROFITTING
There are considerable number of buildings that do not meet the requirements of current design
standards because of inadequate design or construction errors and need structural upgrading
specially to meet the seismic requirements
Retrofitting is the best solution to strengthen such buildings without replacing them
111 भकपीय रलयमकन SEISMIC EVALUATION
Seismic evaluation is to assess the seismic response of buildings which may be seismically
deficient or earthquake damaged for their future use The evaluation is also helpful in choosing
appropriate retrofitting techniques
The methods available for seismic evaluation of existing buildings can be broadly divided into
two categories
1 Qualitative methods 2 Analytical methods
1111 गणमतरक िरीक QUALITATIVE METHODS
The qualitative methods are based on the available background information of the structures
past performance of similar structures under severe earthquakes visual inspection report some
non-destructive test results etc
Method for Seismic evaluation
Qualitative methods Analytic methods
CapacityDemand
method
Push over
analysis
Inelastic time
history method
Condition
assessment
Visual
inspection
Non-destructive
testing
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The evaluation of any building is a difficult task which requires a wide knowledge about the
structures cause and nature of damage in structures and its components material strength etc
The proposed methodology is divided into three components
1 Condition assessment
It is based on
data collection or information gathering of structures from architectural and structural
drawings
performance characteristics of similar type of buildings in past earthquakes
rapid evaluation of strength drift materials structural components and structural details
2 Visual inspectionField evaluation It is based on observed distress and damage in
structures Visual inspection is more useful for damaged structures however it may also be
conducted for undamaged structures
3 Non-destructive evaluation It is generally carried out for quick estimation of materials
strength determination of the extent of determination and to establish causes remain out of
reach from visual inspection and determination of reinforcement and its location NDT may
also be used for preparation of drawing in case of non-availability
11111 Condition Assessment for Evaluation
The aim of condition assessment of the structure is the collection of information about the
structure and its past performance characteristics to similar type of structure during past
earthquakes and the qualitative evaluation of structure for decision-making purpose More
information can be included if necessary as per requirement
(i) Data collection information gathering
Collection of the data is an important portion for the seismic evaluation of any existing building
The information required for the evaluated building can be divided as follows
Building Data
Architectural structural and construction drawings
Vulnerability parameters number of stories year of construction and total floor area
Specification soil reports and design calculations
Seismicity of the site
Construction Data
Identifications of gravity load resisting system
Identifications of lateral load resisting system
Maintenance addition alteration or modifications in structures
Field surveys of the structurersquos existing condition
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Structural Data
Materials
Structural concept vertical and horizontal irregularities torsional eccentricity pounding
short column and others
Detailing concept ductile detailing special confinement reinforcement
Foundations
Non-structural elements
(ii) Past Performance data
Past performance of similar type of structure during the earthquake provides considerable amount
of information for the building which is under evaluation process Following are the areas of
concerns which are responsible for poor performance of buildings during earthquake
Material concerns
Low grade on concrete
Deterioration in concrete and reinforcement
High cement-sand ratio
Corrosion in reinforcement
Use of recycled steel as reinforcement
Spalling of concrete by the corrosion of embedded reinforcing bars
Corrosion related to insufficient concrete cover
Poor concrete placement and porous concrete
Structural concerns
The relatively low stiffness of the frames excessive inter-storey drifts damage to non-
structural items
Pounding column distress possibly local collapse
Unsymmetrical buildings (U T L V) in plan torsional effects and concentration of damage
at the junctures (ie re-entrant corners)
Unsymmetrical buildings in elevation abrupt change in lateral resistance
Vertical strength discontinuities concentrate damage in the ldquosoftrdquo stories
Short column
Detailing concerns
Large tie spacing in columns lack of confinement of concrete core shear failures
Insufficient column lengths concrete to spall
Locations of inadequate splices brittle shear failure
Insufficient column strength for full moment hinge capacity brittle shear failure
Lack of continuous beam reinforcement hinge formation during load reversals
Inadequate reinforcing of beam column joints or location of beam bar splices at columns
joint failures
Improper bent-up of longitudinal reinforcing in beams as shear reinforcement shear failure
during load reversal
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110
Foundation dowels that are insufficient to develop the capacity of the column steel above
local column distress
(iii) Seismic Evaluation Data
Seismic evaluation of data will provide a general idea about the building performance during an
earthquake The criteria of evaluation of building will depend on materials strength and ductility
of structural components and detailing of reinforcement
Material Evaluation
Buildings height gt 3 stories minimum grade concrete M 20 desirable M 30 to M 40
particularly in columns of lower stories
Maximum grade of steel should be Fe 415 due to adequate ductility
No significant deterioration in reinforcement
No evidence of corrosion or spalling of concrete
Structural components
Evaluation of columns shear strength and drift check for permissible limits
Evaluation of plan irregularities check for torsional forces and concentration of forces
Evaluation of vertical irregularities check for soft storey mass or geometric discontinuities
Evaluation of beam-column joints check for strong column-weak beams
Evaluation of pounding check for drift control or building separation
Evaluation of interaction between frame and infill check for force distribution in frames and
overstressing of frames
(i) Flexural members
Limitation of sectional dimensions
Limitation on minimum and maximum flexural reinforcement at least two continuous
reinforced bars at top and bottom of the members
Restriction of lap splices
Development length requirements for longitudinal bars
Shear reinforcement requirements stirrup and tie hooks tie spacing bar splices
(ii) Columns
Limitation of sectional dimensions
Longitudinal reinforcement requirement
Transverse reinforcement requirements stirrup and tie hooks column tie spacing
column bar splices
Special confining requirements
(iii) Foundation
Column steel doweled into the foundation
Non-structural components
Cornices parapet and appendages are anchored
Exterior cladding and veneer are well anchored
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111
11112 Field Evaluation Visual Inspection Method
The procedure for visual inspection method is as below
Equipments
Optical magnification allows a detailed view of local areas of distress
Stereomicroscope that allow a three dimensional view of the surface Investigator can
estimate the elevation difference in surface features by calibrating the focus adjustment
screw
Fibrescope and borescopes allow inspection of regions that are inaccessible to the naked eye
Tape to measure the dimension of structure length of cracks
Flashlight to aid in lighting the area to be inspected particularly in post-earthquake
evaluation power failure
Crack comparator to measure the width of cracks at representative locations two types
plastic cards and magnifying lens comparators
Pencil to draw the sketch of cracks
Sketchpad to prepare a representation of wall elevation indicating the location of cracks
spalling or other damage records of significant features such as non-structural elements
Camera for photographs or video tape of the observed cracking
Action
Perform a walk through visual inspection to become familiar with the structure
Gather background documents and information on the design construction maintenance
and operation of structure
Plan the complete investigation
Perform a detailed visual inspection and observe type of damage cracks spalls and
delaminations permanent lateral displacement and buckling or fracture of reinforcement
estimating of drift
Observe damage documented on sketches interpreted to assess the behaviour during
earthquake
Perform any necessary sampling basis for further testing
Data Collection
To identify the location of vertical structural elements columns and walls
To sketch the elevation with sufficient details dimensions openings observed damage such
as cracks spalling and exposed reinforcing bars width of cracks
To take photographs of cracks use marker paint or chalk to highlight the fine cracks or
location of cracks in photographs
Observation of the non-structural elements inter-storey displacement
Limitations
Applicable for surface damage that can be visualised
No identification of inner damage health monitoring of building chang of frequency and
mode shapes
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11113 Non-destructive testing (NDT)
Visual inspection has the obvious limitation that only visible surface can be inspected Internal
defects go unnoticed and no quantitative information is obtained about the properties of the
concrete For these reasons a visual inspection is usually supplemented by NDT methods Other
detailed testing is then conducted to determine the extent and to establish causes
NDT tests for condition assessment of structures
Some methods of field and laboratory testing that may assess the minimum concrete strength and
condition and location of the reinforcement in order to characterize the strength safety and
integrity are
(i) Rebound hammer Swiss hammer
The rebound hammer is the most widely used non-destructive device for quick surveys to assess
the quality of concrete In 1948 Ernest Schmidt a Swiss engineer developed a device for testing
concrete based upon the rebound principal strength of in-place concrete comparison of concrete
strength in different locations and provides relative difference in strength only
Limitations
Not give a precise value of compressive strength provide estimate strength for comparison
Sensitive to the quality of concrete carbonation increases the rebound number
More reproducible results from formed surface rather than finished surface smooth hard-
towelled surface giving higher values than a rough-textured surface
Surface moisture and roughness also affect the reading a dry surface results in a higher
rebound number
Not take more than one reading at the same spot
(ii) Penetration resistance method ndash Windsor probe test
Penetration resistance methods are used to determine the quality and compressive strength of in-
situ concrete It is based on the determination of the depth of penetration of probes (steel rods or
pins) into concrete by means of power-actuated driver This provides a measure of the hardness
or penetration resistance of the material that can be related to its strength
Limitations
Both probe penetration and rebound hammer test provide means of estimating the relative
quality of concrete not absolute value of strength of concrete
Probe penetration results are more meaningful than the results of rebound hammer
Because of greater penetration in concrete the prove test results are influenced to a lesser
degree by surface moisture texture and carbonation effect
Probe test may be the cause of minor cracking in concrete
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(iii) Rebar locatorconvert meter
It is used to determine quantity location size and condition of reinforcing steel in concrete It is
also used for verifying the drawing and preparing as-built data if no previous information is
available These devices are based on interaction between the reinforcing bars and low frequency
electromagnetic fields Commercial convert meter can be divided into two classes those based
on the principal of magnetic reluctance and those based on eddy currents
Limitations
Difficult to interpret at heavy congestion of reinforcement or when depth of reinforcement is
too great
Embedded metals sometimes affect the reading
Used to detect the reinforcing bars closest to the face
(iv) Ultrasonic pulse velocity
It is used for determination the elastic constants (modulus of elasticity and Poissonrsquos ratio) and
the density By conducting tests at various points on a structure lower quality concrete can be
identified by its lower pulse velocity Pulse-velocity measurements can detect the presence of
voids of discontinuities within a wall however these measurements can not determine the depth
of voids
Limitations
Moisture content an increase in moisture content increases the pulse velocity
Presence of reinforcement oriented parallel to the pulse propagation direction the pulse may
propagate through the bars and result is an apparent pulse velocity that is higher than that
propagating through concrete
Presence of cracks and voids increases the length of the travel path and result in a longer
travel time
(v) Impact echo
Impact echo is a method for detecting discontinuities within the thickness of a wall An impact-
echo test system is composed of three components an impact source a receiving transducer and
a waveform analyzer or a portable computer with a data acquisition
Limitations
Accuracy of results highly dependent on the skill of the engineer and interpreting the results
The size type sensitivity and natural frequency of the transducer ability of FFT analyzer
also affect the results
Mainly used for concrete structures
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(vi) Spectral analysis of surface waves (SASW)
To assess the thickness and elastic stiffness of material size and location of discontinuities
within the wall such as voids large cracks and delimitations
Limitations
Interpretation of results is very complex
Mainly used on slab and other horizontal surface to determine the stiffness profiles of soil
sites and of flexible and rigid pavement systems measuring the changes in elastic properties
of concrete slab
(vii) Penetrating radar
It is used to detect the location of reinforcing bars cracks voids or other material discontinuities
verify thickness of concrete
Limitations
Mainly used for detecting subsurface condition of slab-on-grade
Not useful for detecting the small difference in materials
Not useful for detecting the size of bars closely spaced bars make difficult to detect features
below the layer of reinforcing steel
1112 ववशलषणमतरक िरीक ANALYTICAL METHODS
Analytical methods are based on considering capacity and ductility of the buildings which are
based on detailed dynamic analysis of buildings The methods in this category are
capacitydemand method pushover analysis inelastic time history analysis etc Brief discussions
on the method of evaluation are as follows
11121 CapacityDemand (CD) method
The forces and displacements resulting from an elastic analysis for design earthquake are
called demand
These are compared with the capacity of different members to resist these forces and
displacements
A (CD) ratio less than one indicate member failure and thus needs retrofitting
When the ductility is considered in the section the demand capacity ratio can be equated to
section ductility demand of 2 or 3
The main difficulty encountered in using this method is that there is no relationship between
member and structure ductility factor because of non-linear behaviour
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11122 Push Over Analysis
The push over analysis of a structure is a static non-linear analysis under permanent vertical
loads and gradually increasing lateral loads
The equivalent static lateral loads approximately represent earthquake-induced forces
A plot of total base shear verses top displacement in a structure is obtained by this analysis
that would indicate any premature failure or weakness
The analysis is carried out up to failure thus it enables determination of collapse load and
ductility capacity
On a building frame loaddisplacement is applied incrementally the formation of plastic
hinges stiffness degradation and plastic rotation is monitored and lateral inelastic force
versus displacement response for the complete structure is analytically computed
This type of analysis enables weakness in the structure to be identified The decision to
retrofit can be taken on the basis of such studies
11123 Inelastic time-history analysis
A seismically deficient building will be subjected to inelastic action during design earthquake
motion
The inelastic time history analysis of the building under strong ground motion brings out the
regions of weakness and ductility demand in the structure
This is the most rational method available for assessing building performance
There are computer programs available to perform this type of analysis
However there are complexities with regard to biaxial inelastic response of columns
modelling of joints behaviour interaction of flexural and shear strength and modelling of
degrading characteristics of member
The methodology is used to ascertain deficiency and post-elastic response under strong
ground shaking
Fig ndash 111 Strengthening strategies
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112 भवनो की रटरोफिट ग Retrofitting of Building
Retrofitting is to upgrade the strength and structural capacity of an existing structure to enable it
to safely withstand the effect of strong earthquakes in future
1121 सकटरचरल लवल यम गलोबल रटरोफि िरीक Structural Level or Global Retrofit
Methods
Two approaches are used for structural-level retrofitting
(i) Conventional Methods
(ii) Non-conventional methods
Retrofit procedure
Detailed seismic
evaluation
Retrofit
techniques
Seismic capacity
assessment
Selection of retrofit
scheme
Design of retrofit
scheme and detailing
Re-evaluation of
retrofit structure
Addition of infill walls
Addition of new
external walls
Addition of bracing
systems
Construction of wing
walls
Strengthening of
weak elements
Structural Level or Global Member Level or Local
Seismic Base Isolation
Jacketing of beams
Jacketing of columns
Jacketing of beam-
column joints
Strengthening of
individual footings
Seismic Dampers
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11211 Conventional Methods
Conventional Methods are based on increasing the seismic resistance of existing structure The
main categories of these methods are as follow
a) Addition of infilled walls
b) Addition of new external walls
c) Addition of bracing system
d) Construction of wing walls
e) Strengthening of weak elements
112111 Addition of infilled walls
The construction of infill walls within the frames of the load bearing structures as shown in the
example of Fig ndash 112 aims to drastically increase the strength and the stiffness of the structure
This method can also be applied in order to correct design errors in the structure and more
specifically when a large asymmetric distribution of strength or stiffness in elevation or an
eccentricity of stiffness in plan have been recognised
Fig - 112 Addition of infilled wall and wing walls
Fig - 113 Frames and shear wall
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As shown in Fig ndash 114 there are two alternatives methods of adding infill walls Either the infill
wall is simply placed between two existing columns or it is extended around the columns to form
a jacket The second method is specifically recommended in order to increase the strength in this
region In the situation where the existing columns are very weak a steel cage should be placed
around the columns before constructing new walls and column jackets In all cases the base of
any new wall should always be connected to the existing foundation
112112 Addition of new external walls
In some cases strengthening by adding concrete walls can be performed externally This can
often be carried out for functional reasons as for example in cases when the building must be
kept in operation during the intervention works New cast-in-place concrete walls constructed
outside the building can be designed to resist part or all the total seismic forces induced in the
building The new walls are preferably positioned adjacent to vertical elements (columns or
walls) of the building and are connected to the structure by placing special compression tensile
or shear connectors at every floor level of the building As shown in Figure 115 new walls
usually have a L-shaped cross-section and are constructed to be in contact with the external
corners of the building
Fig ndash 114 Two alternative methods of adding infill walls
Fig ndash 115 Schematic arrangement of connections between the existing building and
a new wall (a) plan (b) section of compression connector and (c) section of tension
connector
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It is important to ensure that connectors behave elastically under seismic design action effects
For this reason when designing the connectors a resistance safety factor equal to 14 is
recommended The use of compression and tensile connectors instead of shear connectors is
strongly recommended as much higher forces can be transferred It is essential that the anchorage
areas for the connectors on the existing
building and on the new walls have
enough strength to guarantee the transfer
of forces between new walls and the
existing structures
A very important issue of the above
method concerns the foundation of new
walls Foundation conditions should be
improved if large axial forces can be
induced in new walls during seismic
excitation In addition the construction
of short cantilever beams protruding from
the wall underneath the adjacent beams
at every floor level of the building as
shown in Fig ndash 116 appears to be a good solution
112113 Addition of bracing systems
The construction of bracing within
the frames of the load bearing
structure aims for a high increase
in the stiffness and a considerable
increase in the strength and
ductility of the structure Bracing
is normally constructed from steel
elements rather than reinforced
concrete as the elastic
deformation of steel aids the
absorption of seismic energy
Bracing systems can be used in a similar way as that for
steel constructions and can be applied easily in single-
storey industrial buildings with a soft storey ground floor
level where no or few brick masonry walls exist between
columns
Various truss configurations have been applied in
practice examples of which are K-shaped diamond
shaped or cross diagonal The latter is the most common
and is often the most effective solution
Fig ndash 116 Construction of cantilever beams to
transfer axial forces to new walls (a) plan (b)
section c-c
Fig ndash 117 Reinforced Concrete Building retrofitted
with steel bracing
Fig ndash 118 Steel bracing soft storey
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Use of steel bracing has a potential advantage over other schemes for the following reasons
Higher strength and stiffness can be proved
Opening for natural light can be
made easily
Amount of work is less since
foundation cost may be minimised
Bracing system adds much less
weight to the existing structure
Most of the retrofitting work can
be performed with prefabricated
elements and disturbance to the
occupants may be minimised
112114 Construction of wing wall
The construction of reinforced
concrete wing walls in continuous
connection with the existing columns
of a structure as shown above in
example of Fig ndash 112 is a very
popular technique
As presented in Fig ndash 1110 there are
two alternative methods of connecting
the wing wall to the existing load
bearing structure
In the first method the wall is connected to the column and the beams at the top and the base
of any floor level Steel dowels or special anchors are used for the connection and the
reinforcement of the new wall is welded to the existing reinforcement
In the second method the new wing wall is extended around the column to form a jacket
Obviously in this case stresses at the interface between the new concrete and the existing
column are considerably lower when compared to the first method
Moreover uncertainties regarding the capacity of the connection between the wall and the
column do not affect the seismic performance of the strengthened element Therefore the second
alternative method is strongly recommended
Fig ndash 1110 Construction of reinforced concrete wing
wall
Fig ndash 119 Steel bracing
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112115 Strengthening weak elements
The selective strengthening of weak elements of the
structure aims to avoid a premature failure of the critical
elements of a building and to increase the ductility of the
structure
Usually this method is applied to vertical elements and
is accompanied by the construction of fibre reinforced
polymer (FRP) jackets or as shown in Fig- 1111 steel
cages around the vertical elements
If a strength increase is also required this method can
include the construction of column jackets of shotcrete
or reinforced concrete
11212 Non-conventional methods
These are based on reduction of seismic demands Seismic demands are the force and
displacement resulting from an elastic analysis for earthquake design Incorporation of energy
absorbing systems to reduce seismic demands are as follows
(i) Seismic Base Isolation
(ii) Seismic Dampers
112121 Seismic Base Isolation
Isolation of
superstructure from the
foundation is known as
base isolation
It is the most powerful
tool for passive
structural vibration
control technique
Types of base isolations
Elastomeric Bearings
This is the most widely used Base Isolator
The elastomer is made of either Natural Rubber or Neoprene
The structure is decoupled from the horizontal components of the earthquake ground motion
Fig ndash 1111 Construction of a steel
cage around a vertical element
Fig ndash 1112 Base isolated structures
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Sliding System
a) Sliding Base Isolation Systems
It is the second basic type of isolators
This works by limiting the base shear across the
isolator interface
b) Spherical Sliding Base Isolators
The structure is supported by bearing pads that
have curved surface and low friction
During an earthquake the building is free to
slide on the bearings
c) Friction Pendulum Bearing
These are specially designed base isolators
which works on the
principle of simple
pendulum
It increases the natural time
period of oscillation by
causing the structure to
Fig ndash 1113 Elastomeric Isolators Fig ndash 1114 Steel Reinforced Elastomeric
Isolators
Fig ndash 1115 Metallic Roller Bearing
Fig ndash 1116 Spherical Sliding Base
Isolators
Fig ndash 1117 Cross-section of Friction Pendulum Bearing
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slide along the concave inner surface through the frictional interface
It also possesses a re-centering capability
Typically bearings measure 10 m (3 feet) in dia 200 mm (8 inches) in height and weight
being 2000 pounds
d) Advantages of base isolation
Isolate building from ground motion
Building can remain serviceable throughout construction
Lesser seismic loads hence lesser damage to the structure
Minimal repair of superstructure
Does not involve major intrusion upon existing superstructure
e) Disadvantages of base isolation
Expensive
Cannot be applied partially to structures unlike other retrofitting
Challenging to implement in an efficient manner
Allowance for building displacements
Inefficient for high rise buildings
Not suitable for buildings rested on soft soil
112122 Seismic Dampers
Seismic dampers are used in place of structural elements like diagonal braces for controlling
seismic damage in structures
It partly absorbs the seismic energy and reduces the motion of buildings
Types
Viscous Dampers Energy is absorbed by silicon-based fluid passing between piston-
cylinder arrangement
Fig -1118 Cross-section of a Viscous Fluid Damper
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Friction Dampers Energy is absorbed
by surfaces with friction between
rubbing against each other
Yielding Dampers Energy is absorbed
by metallic components that yield
1122 सदसकय सकिर यम सकथमनीय ररटरोफमइ िरीक Member Level or Local Retrofit Methods
The member level retrofit or local retrofit approach is to upgrade the strength of the members
which are seismically deficient This approach is more cost effective as compared to the
structural level retrofit
Jacketing
The most common method of enhancing the individual member strength is jacketing It includes
the addition of concrete steel or fibre reinforced polymer (FRP) jackets for use in confining
reinforced concrete columns beams joints and foundation
Types of jacketing
(1) Concrete jacketing (2) Steel jacketing (3) Strap jacketing
Fig ndash 1119 Friction Dampers
Fig ndash 1120 Yielding Dampers
Fig ndash 1121 Type of Jacketing
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11221 Member level Jacketing
(i) Jacketing of Columns
Different methods of column jacketing are as shown in Figures below
Fig ndash 1122 (b) Column with
CFRP (Carbon Fibre
Reinforced Polymer) Wrap
Fig ndash 1122 (c) Column with Steel Fig ndash 1122 (d) Column with
Jacketing Steel Caging
Fig ndash 1122 (a) Reinforced Concrete Jacketing
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Fig ndash 1122 (e) Construction techniques for Fig ndash 1122 (f) Local strengthening of RC
column jacketing Columns
Fig ndash 1122 (g) Details for provision of longitudinal reinforcement
Fig ndash 1122 (h) Different methods of column jacketing
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(ii) Jacketing of Beam
(iii) Jacketing of Beam-Column Joint
Fig ndash 1123 Different ways of beam jacketing
Fig ndash 1124 Continuity of longitudinal steel in jacketed beams
Fig ndash 1125 Steel cage assembled in the joint
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11222 Table showing the details of reinforced concrete jacketing
Properties of jackets match with the concrete of the existing structure
compressive strength greater than that of the existing
structures by 5 Nmm2 (50 kgcm
2) or at least equal to that
of the existing structure
Minimum width of
jacket 10 cm for concrete cast-in-place and 4 cm for shotcrete
If possible four sided jacket should be used
A monolithic behaviour of the composite column should be
assured
Narrow gap should be provided to prevent any possible
increase in flexural capacity
Minimum area of
longitudinal
reinforcement
3Afy where A is the area of contact in cm2 and fy is in
kgcm2
Spacing should not exceed six times of the width of the new
elements (the jacket in the case) up to the limit of 60 cm
Percentage of steel in the jacket with respect to the jacket
area should be limited between 0015 and 004
At least a 12 mm bar should be used at every corner for a
four sided jacket
Minimum area of
transverse
reinforcement
Designed and spaced as per earthquake design practice
Minimum bar diameter used for ties is not less than 10 mm
diameter anchorage
Due to the difficulty of manufacturing 135 degree hooks on
the field ties made up of multiple pieces can be used
Shear stress in the
interface Provide adequate shear transfer mechanism to assured
monolithic behaviour
A relative movement between both concrete interfaces
(between the jacket and the existing element) should be
prevented
Chipping the concrete cover of the original member and
roughening its surface may improve the bond between the
old and the new concrete
For four sided jacket the ties should be used to confine and
for shear reinforcement to the composite element
For 1 2 3 side jackets as shown in Figures special
reinforcement should be provided to enhance a monolithic
behaviour
Connectors Connectors should be anchored in both the concrete such that
it may develop at least 80 of their yielding stress
Distributed uniformly around the interface avoiding
concentration in specific locations
It is better to use reinforced bars (rebar) anchored with epoxy
resins of grouts as shown in Figure (a)
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11223 Practical aspects in choosing appropriate techniques
Certain issues of practical importance that may help to avoid mistakes in choosing the
appropriate technique are as follows
1) The strengthening of columns by using FRPs or steel jackets is unsuitable for flexible
structures where failure would be controlled by deflection In this case the strengthening
should aim to increase the stiffness
2) It is not favourable to use steel cages or confine with FRPs when an increase in the flexural
capacity of vertical elements is required
3) The application of confinement (with FRPs or steel) to circular or rectangular columns would
increase the ductility and the shear strength and would limit the slippage of overlapping bars
when the lap length has been found to be insufficient However a significant contribution
cannot be expected for columns of rectangular cross section with a large aspect ratio or those
with L-shaped cross sections
4) In the case of columns that have heavily rusted reinforcement strengthening with FRP
jackets (or the application of epoxy glue) will protect the reinforcement from further
oxidation However if the corrosion of the reinforcement is at an advanced stage it is
probable that strengthening may not stop the premature failure of the element
5) The construction of FRP jackets around vertical elements will increase the ductility but it
cannot increase the buckling resistance of the longitudinal reinforcement bars Thus if the
stirrups are too thin in an existing element failure will probably result from the premature
bending of the vertical reinforcement In this case local stress concentrations from the
distressed bars will build up between the stirrups and will lead to a local failure of the jacket
Consequently if bending of the vertical reinforcement has been evaluated as the most likely
cause of column failure the preferable choice for strengthening of the element would be to
place a steel cage
6) In areas where the overlapping of reinforcement bars has been found to be inadequate (short
lap lengths) confining the element with FRPs steel cages or steel jackets will improve the
strength and the ductility of the region considerably However even if it improved the
behaviour it is eventually unfeasible to deter the slipping of bars Consequently when the lap
length of bars has been found to be smaller than 30 of code requirements the solution of
welding of bars must be selected Moreover it must be pointed out that confinement cannot
offer anything to longitudinal bars that are not in the corners of the cross section
7) Experimentally the procedure of placing FRP sheets to strengthen weak beam-column joints
has proved to be particularly effective In practice however this technique has been found to
be difficult to apply due to the presence of slabs and transverse beams The same problems
arise when placing steel plates Other techniques such as the construction of reinforced
concrete jackets or the reconstruction of joints with additional interior reinforcement appear
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to be more beneficial In cases where only a light damage to the joints has been found
repairing with an epoxy resin appears to be particularly effective solution
8) The placing of new concrete in contact with an existing element (by shotcreting and
especially by pouring) will require prior aggravation of the old surface to a depth of at least 6
mm This should be performed by sandblasting or by using suitable mechanical equipment
(for example a scabbler and not just simply a hammer and a chisel) This is to remove the
exterior weak skin of the concrete and to expose the aggregate
9) When placing a new concrete jacket around an existing column it is not always possible to
follow code requirements and place
internal rectangular stirrups to enclose
the middle longitudinal bars as shown
in Fig-1126(a) In this case it is
proposed to place two middle bars in
each side of the jacket so that
octagonal stirrups can be easily
placed as demonstrated in
Fig-1126(b)
In the case where columns have a cross section
with a large aspect ratio the middle longitudinal
bars can be connected by drilling holes through
the section in order to place a S-shaped stirrup as
shown in Fig ndash 1127 After placing stirrups the
remaining void can be filled with epoxy resin In
order to ease placement the S-shaped stirrup can
be prefabricated with one hook and after placing
the second hook can be formed by hand
10) If a thin concrete jacket is to be
placed around a vertical element
and the 135 deg hooks at the ends
of the stirrups are impeded by the
old column it would be
acceptable to decrease the hook
anchorage from 10 times the bar
diameter to 5 or 6 times the bar
diameter as shown in
Fig ndash 1128(a) Otherwise the
ends the stirrups should be
welded together or connected
with special contacts (clamps) as
presented in Fig ndash 1128(b) that have now appeared on the market
(a) (b)
Fig ndash 1126 Placement of internal stirrups in
rectangular cross section
Fig ndash 1127 Placement of an internal
stirrup in a rectangular cross section
with a large aspect ratio
(a) (b)
Fig ndash 1128 Reducing hook lengths and welding the
ends of stirrups
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11) When constructing a jacket around a column it is
important to also strengthen the column joint As shown
in Fig ndash 1129 this can be accomplished by where
possible extending the longitudinal reinforcement bars
around the joint In addition as also shown in
Fig ndash 1129 stirrups must be placed in order to confine
the concrete of the jacket around the joint
In the case where the joint has been found to be
particularly weak a steel diagonal collar can be placed
around the joint before placing the reinforcement as
shown in Fig ndash 1130
12) It is preferable that a new concrete jacket is placed
continuously from the foundation to the top of the building
If this is not possible (due to maintaining the functioning of
the building) it is usual to stop the jacket at the top of the
ground floor level In this case there is a need to anchor the
jacketrsquos longitudinal bars to the existing column This can
be achieved by anchoring a steel plate to the base of the
column of the floor level above and then welding the
longitudinal bars to the anchor plate as shown in Fig ndash
1131
13) In the case where there is a need to reconstruct a heavily damaged column after first shoring
up the column all the defective concrete must be removed so that only good concrete
Fig ndash 1129 Strengthening the
column joint
Fig ndash 1130 Placing a steel diagonal collar
around a weak column joint
Fig ndash 1131 Removal of
defective concrete from a
heavily damaged column
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remains as shown in Fig ndash 1132 Any
buckled reinforcement bars must be welded
to the existing bars Finally the column can
be recast by placing a special non-shrink
concrete
14) In order to anchor new reinforcement bars dowels or anchors with the use of epoxy glue the
diameter of holes drilled into the existing concrete should be roughly 4 mm larger than the
diameter of the bar The best way to remove dust from drilled holes would be to spray water
at the back of the hole The best results (higher adhesive forces) are achieved when the walls
of the hole have been roughened slightly with a small wire brush
15) Care is required when shotcreting in the presence of reinforcement There is a danger of an
accumulation of material building up behind the bars This is usually accredited to material
sticking to the face of bars and may be due to either a low velocity a large firing distance or
insufficient pressure from the compressor
16) The placing of steel plates and especially FRP sheets or fabrics requires special preparation of
the concrete surface to which they will be stuck The rounding of corners and the removal of
surface abnormalities constitute minimal conditions for the application of this technique
17) Two constructional issues that concern the connection of new walls to the old frame require
particular attention The first problem is due to the shrinkage of the new concrete and the
appearance of cracks at the top of the new wall immediately below the old beam in the
region where a good contact between surfaces is essential Here the problem of shrinkage
can be usually dealt with by placing concrete of a particular composition where special
admixtures (for example expansive cements) have been used Alternatively the new wall
could be placed to about 20 cm below the existing beam and after more than 7 days (taking
into account temperature and how new concrete shrinks with time) the void can be filled
with an epoxy or polyster mortar In some cases depending on site conditions (ease of access
dry conditions etc) the new wall can be placed to a height of 2 to 5 mm below the beam and
the void filled with resin glue using the technique of resin injection The second problem
concerns the case of walls from ready-mix concrete and the difficulty of placing the higher
part of the wall due to insufficient access For this reason alone the use of shotcrete should
be the preferred option
Fig ndash 1132 Welding longitudinal bars to an
anchor plate
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113 आरसी भवनो क घ को र समरमनय भकपी कषतियम और उनक उपचमर Common
seismic damage in components of RC Buildings and their remedies
Possible damages in component of RC Buildings which are frequently observed after the
earthquakes are as follows
(i) R C Column
The most common modes of failure of column are as follows
Mode -1 Formation of plastic hinge at the base of ground level columns
Mechanism The column when subjected to seismic
motion its concrete begins to disintegrate and the
load carried by the concrete shifts to longitudinal
reinforcement of the column This additional load
causes buckling of longitudinal reinforcement As a
result the column shortens and looses its ability to
carry even the gravity load
Reasons Insufficient confinement length and
improper confinement in plastic hinge region due to
smaller numbers of ties
Remedies This type of damage is sensitive to the cyclic moments generated during the
earthquake and axial load intensity Consideration is to be paid on plastic hinge length or length
of confinement
Mode ndash 2 Diagonal shear cracking in mid span of columns
Mechanism In older reinforced
concrete building frames column
failures were more frequent since
the strength of beams in such
constructions was kept higher than
that of the columns This shear
failure brings forth loss of axial
load carrying capacity of the
column As the axial capacity
diminishes the gravity loads carried by the column are transferred to neighbouring elements
resulting in massive internal redistribution of forces which is also amplified by dynamic effects
causing spectacular collapse of building
Reason Wide spacing of transverse reinforcement
Remedies To improve understanding of shear strength as well as to understand how the gravity
loads will be supported after a column fails in shear
Fig ndash 1133 Formation of plastic hinge at
the base
Fig ndash 1134 Diagonal shear cracking in mid span of
columns
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Mode ndash 3 Shear and splice failure of longitudinal reinforcement
Mechanism Splices of column
longitudinal reinforcement in
older buildings were
commonly designed for
compression only with
relatively light transverse
reinforcement enclosing the
lap
Under earthquake motion the
longitudinal reinforcement may
be subjected to significant tensile stresses which require lap lengths for tension substantially
exceeding those for compression As a result slip occurs along the splice length with spalling of
concrete
Reasons Deficient lap splices length of column longitudinal reinforcement with lightly spaced
transverse reinforcement particularly if the splices just above the floor slab especially the splices
just above the floor slab which is very common in older construction
Remedies Lap splices should be provided only in the center half of the member length and it
should be proportionate to tension splice Spacing of transverse reinforcement as per IS
139291993
Mode ndash 4 Shear failures in captive columns and short columns
Captive column Column whose deforming ability is restricted and only a fraction of its height
can deform laterally It is due to presence of adjoining non-structural elements columns at
slopping ground partially buried basements etc
Fig - 1135 Shear and splice failure of longitudinal
reinforcement
Fig ndash 1136 Restriction to the Lateral
Displacement of a Column Creating a Captive-
Column Effect
Fig ndash 1137 Captive-column effect in a
building on sloping terrain
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A captive column is full storey slender column whose clear height is reduced by its part-height
contact with a relatively stiff non-structural element such as a masonry infill wall which
constraints its lateral deformation over
the height of contract
The captive column effect is caused by
a non-intended modification to the
original structural configuration of the
column that restricts the ability of the
column to deform laterally by partially
confining it with building components
The column is kept ldquocaptiverdquo by these
components and only a fraction of its
height can deform laterally
corresponding to the ldquofreerdquo portion
thus the term captive column Figure
as given below shows this situation
Short column Column is made shorter than neighbouring column by horizontal structural
elements such as beams girder stair way landing slabs use of grade beams and ramps
Fig ndash 1138 Typical captive-column failure Fig ndash 1139 Column damage due to
captive- column effect
Fig ndash 1140 Captive column caused by ventilation
openings in a partially buried basement
Fig ndash 1141 Short column created by
a stairway landing
Fig ndash 1142 Shear failures in captive columns
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For split-level buildings in order to circumvent the short-column effect the architect should
avoid locating a frame at the vertical plane where the transition between levels occurs For
buildings on slopes special care should be exercised to locate the sloping retaining walls in such
a way that no captive-column effects are induced Where stiff non-structural walls are still
employed these walls should be separated from the structure and in no case can they be
interrupted before reaching the full height of the adjoining columns
Mechanism A reduction in the clear height of captive or short columns increases the lateral
stiffness Therefore these columns are subjected to larger shear force during the earthquake since
the storey shear is distributed in proportion to lateral stiffness of the same floor If these columns
reinforced with conventional longitudinal and transverse reinforcement and subjected to
relatively high axial loading fail by splitting of concrete along their diagonals if the axial
loading level is low the most probable mode of failure is by shear sliding along full depth cracks
at the member ends Moreover in the case of captive column is so effective that usually damage
is shifted to the short non-confined upper section of the column
Reasons Large shear stresses when the structure is subjected to lateral forces are not accounted
for in the standard frame design procedure
Remedies The best solution for captive column or short column is to avoid the situation
otherwise use separation gap in between the non-structural elements and vertical structural
element with appropriate measures against out-of-plane stability of the masonry wall
(ii) R C Beams
The shear-flexure mode of failure is most commonly observed during the earthquakes which is
described as below
Mode ndash 5 Shear-flexure failure
Mechanism Two types of plastic hinges may form in the beams of multi-storied framed
construction depending upon the span of
beams In case of short beams or where
gravity load supported by the beam is
low plastic hinges are formed at the
column ends and damage occurs in the
form of opening of a crack at the end of
beam otherwise there is formation of
plastic hinges at and near end region of
beam in the form of diagonal shear
cracking
Reasons Lack of longitudinal compressive reinforcement infrequent transverse reinforcement in
plastic hinge zone bad anchorage of the bottom reinforcement in to the support or dip of the
longitudinal beam reinforcement bottom steel termination at face of column
Fig ndash 1143 Shear-flexure failure
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Remedies Adequate flexural and shear strength must be provided and verification by design
calculation is essential The beams should not be too stiff with respect to adjacent columns so
that the plastic hinging will occur in beam rather than in column To ensure that the plastic hinges
zones in beams have adequate ductility the following considerations must be considered
Lower and upper limits on the amount of longitudinal flexural tension steel
A limit on the ration of the steel on one side of the beam to that of on the other side
Minimum requirements for the spacing and size of stirrups to restrain buckling of the
longitudinal reinforcement
(iii) R C Beam-Column Joints
The most common modes of failure in beam-column joint are as follows
Mode ndash 6 shear failure in beam-column joint
Mechanism The most common
failure observed in exterior joints are
due to either high shear or bond
(anchorage) under severe
earthquakes Plastic hinges are
formed in the beams at the column
faces As a result cracks develop
throughout the overall beam depth
Bond deterioration near the face of
the column causes propagation of
beam reinforcement yielding in the joint and a shortening of the bar length available for force
transfer by bond causing horizontal bar slippage in the joint In the interior joint the beam
reinforcement at both the column faces undergoes different stress conditions (compression and
tension) because of opposite sights of seismic bending moments results in failure of joint core
Reasons Inadequate anchorage of flexural steel in beams lack of transverse reinforcement
Remedies Exterior Joint ndash The provision on anchorage stub for the beam reinforcement
improves the performance of external joints by preventing spalling of concrete cover on the
outside face resulting in loss of flexural strength of the column This increases diagonal strut
action as well as reduces steel congestion as the beam bars can be anchored clear of the column
bars
(iv) R C Slab
Generally slab on beams performed well during earthquakes and are not dangerous but cracks in
slab creates serious aesthetic and functional problems It reduces the available strength stiffness
and energy dissipation capacity of building for future earthquake In flat slab construction
punching shear is the primary cause of failure The common modes of failure are
Fig - 1144 Shear failure in beam-column joint
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Mode ndash 7 Shear cracking in slabs
Mechanism Damage to slab oftenly
occurs due to irregularities such as large
openings at concentration of earthquake
forces close to widely spaced shear
walls at the staircase flight landings
Reasons Existing micro cracks which
widen due to shaking differential
settlement
Remedies
Use secondary reinforcement in the bottom of the slab
Avoid the use of flat slab in high seismic zones provided this is done in conjunction with a
stiff lateral load resisting system
(v) R C Shear Walls
Shear walls generally performed well during the earthquakes Four types of failure modes are
generally observed
Mode ndash 8 Four types of failure modes are generally observed
(i) Diagonal tension-compression failure in the form of cross-shaped shear cracking
(ii) Sliding shear failure cracking at interface of new and old concrete
(iii) Flexure and compression in bottom end region of wall and finally
(iv) Diagonal tension in the form of X shaped cracking in coupling beams
Fig ndash 1145 Shear cracking in slabs
Fig ndash 1146 Diagonal tension-compression Sliding shear Flexure and compression
failure
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Mechanism Shear walls are subjected to shear and flexural deformation depending upon the
slenderness ratio Therefore the damage in shear walls may generally occurs due to inadequate
shear and flexure capacity of wall Slender walls are governed by their flexural strength and
cracking occurs in the form of yielding of main flexure reinforcement in the plastic hinge region
normally at the base of the wall Squat walls are governed by their shear strength and failure
takes place due to diagonal tension or diagonal compression in the form of inclined cracking
Coupling beams between shear walls or piers may also damage due to inadequate shear and
flexure capacity Sometimes damage occurs at the construction joints in the form of slippage and
related drift
Reasons
Flexuralboundary compression failure Inadequate transverse confining reinforcement to the
main flexural reinforcement near the outer edge of wall in boundary elements
Flexurediagonal tension Inadequate horizontal shear reinforcement
Sliding shear Absence of diagonal reinforcement across the potential sliding planes of the
plastic hinge zone
Coupling beams Inadequate stirrup reinforcement and no diagonal reinforcement
Construction joint Improper bonding between two surfaces
Remedies
The concrete shear walls must have boundary elements or columns thicker than walls which
will carry the vertical load after shear failure of wall
A proper connection between wall versus diaphragm as well as wall versus foundation to
complete the load path
Proper bonding at construction joint in the form of shear friction reinforcement
Provision of diagonal steel in the coupling beam
Fig ndash 1147 Diagonal tension in the form of X shaped
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(v) Infill Walls
Infill panels in reinforced concrete frames are the cause of unequal distribution of lateral forces
in the different frames of a building producing vertical and horizontal irregularities etc the
common mode of failure of infill masonry are in plane or shear failure
Mode ndash 9 Shear failure of masonry infill
Mechanism Frame with infill possesses much more lateral stiffness than the bare frame and
hence initially attracts most of the lateral force during an earthquake Being brittle the infill
starts to disintegrate as soon as its strength is reached Infills that were not adequately tied to the
surrounding frames sometimes dislodges by out-of-plane seismic excitations
Reasons Infill causes asymmetry of load application resulting in increased torsional forces and
changes in the distribution of shear forces between lateral load resisting system
Remedies Two strategies are possible either complete separation between infill walls and frame
by providing separation joint so that the two systems do not interact or complete anchoring
between frame and infill to act as an integral unit Horizontal and vertical reinforcement may also
be used to improve the strength stiffness and deformability of masonry infill walls
(vi) Parapets
Un-reinforced concrete parapets with large height-to-thickness ratio and not in proper anchoring
to the roof diaphragm may also constitute a hazard The hazard posed by a parapet increases in
direct proportion to its height above building base which has been generally observed
The common mode of failure of parapet wall is against out-of-plane forces which is described as
follows
Mode ndash 10 Brittle flexure out-of-plane failure
Mechanism Parapet walls are acceleration sensitive in the out-of-plane direction the result is
that they may become disengaged and topple
Fig ndash 1148 Shear failure of masonry infill
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141
Reasons Not properly braced
Remedies Analysed for acceleration forces and braced and connected with roof diaphragm
114 चचनमई सरचनमओ की रटरोफिट ग Retrofitting of Masonry Structures
(a) Principle of Seismic Safety of Masonry Buildings
Integral box action
Integrity of various components
- Roof to wall
- Wall to wall at corners
- Wall to foundation
Limit on openings
(b) Methods for Retrofitting of Masonry Buildings
Repairing (Improving existing masonry strength)
Stitching of cracks
Grouting with cement or epoxy
Use of CFRP (Carbon Fibre Reinforced Polymer) strips
Fig ndash 1149 Brittle flexure out-of-plane failure
(a) (b)
Fig ndash 1150 (a) Stitching of cracks Fig ndash 1150 (b) Repair of damaged member in
masonry walls
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(c) Retrofitting of Earthquake vulnerable buildings
External binding or jacketing
Shotcreting
Strengthening of wall intersections
Strengthening by cross wall
Strengthening by buttresses
Strengthening of arches
Fig ndash 1151 Integral Box action
(a) (b)
Fig - 1152 (a) Strengthening of Wall Fig - 1152 (b) Strengthening by
intersections cross wall
(a) (b)
Fig ndash 1153 (a) Strengthening by Fig ndash 1153 (b) Strengthening of Arches
Buttresses
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पररलिष Annexure ndash I
भारिीय भको पी सोतििाएा Indian Seismic Codes
Development of building codes in India started rather early Today India has a fairly good range
of seismic codes covering a variety of structures ranging from mud or low strength masonry
houses to modern buildings However the key to ensuring earthquake safety lies in having a
robust mechanism that enforces and implements these design code provisions in actual
constructions
भको पी तिजाइन कोि का मितव Importance of Seismic Design Codes
Ground vibrations during earthquakes cause forces and deformations in structures Structures
need to be designed to withstand such forces and deformations Seismic codes help to improve
the behaviour of structures so that they may withstand the earthquake effects without significant
loss of life and property An earthquake-resistant building has four virtues in it namely
(a) Good Structural Configuration Its size shape and structural system carrying loads are such
that they ensure a direct and smooth flow of inertia forces to the ground
(b) Lateral Strength The maximum lateral (horizontal) force that it can resist is such that the
damage induced in it does not result in collapse
(c) Adequate Stiffness Its lateral load resisting system is such that the earthquake-induced
deformations in it do not damage its contents under low-to moderate shaking
(d) Good Ductility Its capacity to undergo large deformations under severe earthquake shaking
even after yielding is improved by favourable design and detailing strategies
Seismic codes cover all these aspects
भारिीय भको पी सोतििाएा Indian Seismic Codes
Seismic codes are unique to a particular region or country They take into account the local
seismology accepted level of seismic risk building typologies and materials and methods used
in construction The first formal seismic code in India namely IS 1893 was published in 1962
Today the Bureau of Indian Standards (BIS) has the following seismic codes
1 IS 1893 (Part I) 2002 Indian Standard Criteria for Earthquake Resistant Design of
Structures (5 Revision)
2 IS 4326 1993 Indian Standard Code of Practice for Earthquake Resistant Design and
Construction of Buildings (2nd Revision)
3 IS 13827 1993 Indian Standard Guidelines for Improving Earthquake Resistance of
Earthen Buildings
4 IS 13828 1993 Indian Standard Guidelines for Improving Earthquake Resistance of Low
Strength Masonry Buildings
5 IS 13920 1993 Indian Standard Code of Practice for Ductile Detailing of Reinforced
Concrete Structures Subjected to Seismic Forces
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6 IS 13935 1993 Indian Standard Guidelines for Repair and Seismic Strengthening of
Buildings
The regulations in these standards do not ensure that structures suffer no damage during
earthquake of all magnitudes But to the extent possible they ensure that structures are able to
respond to earthquake shakings of moderate intensities without structural damage and of heavy
intensities without total collapse
IS 1893 (Part I) 2002
IS 1893 is the main code that provides the seismic zone map and specifies seismic design force
This force depends on the mass and seismic coefficient of the structure the latter in turn
depends on properties like seismic zone in which structure lies importance of the structure its
stiffness the soil on which it rests and its ductility For example a building in Bhuj will have
225 times the seismic design force of an identical building in Bombay Similarly the seismic
coefficient for a single-storey building may have 25 times that of a 15-storey building
The revised 2002 edition Part 1 of IS1893 contains provisions that are general in nature and
those applicable for buildings The other four parts of IS 1893 will cover
a) Liquid-Retaining Tanks both elevated and ground supported (Part 2)
b) Bridges and Retaining Walls (Part 3)
c) Industrial Structures including Stack Like Structures (Part 4) and
d) Dams and Embankments (Part 5)
These four documents are under preparation In contrast the 1984 edition of IS1893 had
provisions for all the above structures in a single document
Provisions for Bridges
Seismic design of bridges in India is covered in three codes namely IS 1893 (1984) from the
BIS IRC 6 (2000) from the Indian Roads Congress and Bridge Rules (1964) from the Ministry
of Railways All highway bridges are required to comply with IRC 6 and all railway bridges
with Bridge Rules These three codes are conceptually the same even though there are some
differences in their implementation After the 2001 Bhuj earthquake in 2002 the IRC released
interim provisions that make significant improvements to the IRC6 (2000) seismic provisions
IS 4326 1993 (Reaffirmed 2003)
This code covers general principles for earthquake resistant buildings Selection of materials
and special features of design and construction are dealt with for the following types of
buildings timber constructions masonry constructions using rectangular masonry units and
buildings with prefabricated reinforced concrete roofingflooring elements The code
incorporates Amendment No 3 (January 2005)
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IS 13827 1993 and IS 13828 1993
Guidelines in IS 13827 deal with empirical design and construction aspects for improving
earthquake resistance of earthen houses and those in IS 13828 with general principles of
design and special construction features for improving earthquake resistance of buildings of
low-strength masonry This Masonry includes burnt clay brick or stone masonry in weak
mortars like clay-mud These standards are applicable in seismic zones III IV and V
Constructions based on them are termed non-engineered and are not totally free from collapse
under seismic shaking intensities VIII (MMI) and higher Inclusion of features mentioned in
these guidelines may only enhance the seismic resistance and reduce chances of collapse
IS 13920 1993 (Reaffirmed 2003)
In India reinforced concrete structures are designed and detailed as per the Indian Code IS 456
(2002) However structures located in high seismic regions require ductile design and
detailing Provisions for the ductile detailing of monolithic reinforced concrete frame and shear
wall structures are specified in IS 13920 (1993) After the 2001 Bhuj earthquake this code has
been made mandatory for all structures in zones III IV and V Similar provisions for seismic
design and ductile detailing of steel structures are not yet available in the Indian codes
IS 13935 1993
These guidelines cover general principles of seismic strengthening selection of materials and
techniques for repairseismic strengthening of masonry and wooden buildings The code
provides a brief coverage for individual reinforced concrete members in such buildings but
does not cover reinforced concrete frame or shear wall buildings as a whole Some guidelines
are also laid down for non-structural and architectural components of buildings
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पररलिष Annexure ndash II
Checklist Multiple Choice Questions for Points to be kept in mind during
Construction of Earthquake Resistant Building
S No Description Observer Remarks
1 Seismic Zone in which building is located
i) Zone II ndash Least Seismically Prone Region
ii) Zone III ndash
iii) Zone IV ndash
iv) Zone V ndash Most Seismically Prone Region
Choose Zone
2 Environment condition to which building is exposed
a) Mild b) Moderate c) Severe d) Very Severe e) Extreme
Choose Condition
3 Whether the building is located in Flood Zone YesNo
4 Whether the building is located in Land Slide Zone ie building is on
hill slope or Plane Area
YesNo
5 Type of soil at founding level
a) Rock or Hard Soil
b) Medium Soil
c) Soft Soil
Choose type of soil
6 Type of Building
I) Load Bearing Masonry Building
a) Brick Masonry Construction
b) Stone Masonry construction
II) RCC Framed Structure
a) Regular frame
b) Regular Frame with shear wall
c) Irregular Frame
d) Irregular Frame with shear wall
e) Soft Story Building
Choose type of
building
7 No of Story above Ground Level with provision of Future Extension Mention Storey
8 Category of Building considering Seismic Zone and Importance
Factor (As per Table ndash 102)
i) Category B ndash Building in Seismic Zone II with Importance Factor
10
ii) Category E- Building in Seismic Zone II with Importance Factor
10 and 150
Choose category
9 Bricks should not have compressive strength less than 350 MPa YesNo
10 Minimum wall thickness of brick masonry
i) 1 Brick ndash Single Storey Construction
ii) 1 frac12 Brick ndash In bottom storey up to 3 storey construction amp
1 Brick in top storey with brick masonry
Choose appropriate
11 Height of building is restricted to
i) For A B amp C categories ndash G+2 with flat roof G+1 plus anti for
pitched roof when height of each story not exceed 3 m
ii) D category ndash G+1 with flat Roof
- Ground plus attic for pitched roof
Choose appropriate
12 Max Height of Brick masonry Building ndash 15 m (max 4 storey) YesNo
13 Mortar mix shall be as per Table ndash 102 for category A to E Choose Mortar
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14 Height of Stone Masonry wall
i) For Categories AampB ndash
a) When built in Lime-Sand or Mud mortar
ndash Two storey with flat roof or One Storey plus attic
b) When build in cement sand 16 mortar
- One story higher
ii) For Categories CampD ndash
a) When built in cement Sand 16 Mortar
- Two storey with flat roof or One Storey plus attic for pitched
roof
b) When build in lime sand or Mud mortar
- One story with flat roof or One Story plus attic
Choose appropriate
15 Through stone at full length equal to wall thickness in every 600 mm
lift at not more than 120 m apart horizontally has been provided
YesNo
16 Through stone and Bond Element as per Fig 1024 has been provided YesNo
17 Horizontal Bands
a) Plinth Band
b) Lintel Band
c) Roof Bond
d) Gable Bond
For Over Strengthening Arrangement for Category D amp E Building
have been provided
YesNo
18 Bond shall be made up of Reinforced Concrete of Grade not leaner
than M15 or Reinforced brick work in cement mortar not leaner than
13
YesNo
19 Bond shall be of full width of wall not less than 75 mm in depth and
reinforced with steel as shown in Table ndash 106
YesNo
20 Vertical steel at corners amp junction of wall which are up to 340 mm
(1 frac12 brick) thick shall be provided as shown in Table ndash 101
YesNo
21 General principal for planning building are
i) Building should be as light as possible
ii) All parts of building should be tied together to act as one unit
iii) Projecting part should be avoided
iv) Building having plans with shape L T E and Y shall preferably
be separated in to rectangular parts
v) Structure not to be founded on loose soil which will subside or
liquefy during Earthquake resulting in large differential
settlement
vi) Heavy roofing material should be avoided
vii) Large stair hall shall be separated from Rest of the Building by
means of separation or crumple section
viii) All of the above
ix) None of the above
Choose Correct
22 Structural irregularities may be
i) Horizontal Irregularities
ii) Vertical Irregularities
iii) All of the above
iv) None of the above
Choose Correct
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23 Horizontal Irregularities are
i) Asymmetrical plan shape (eg LTUF)
ii) Horizontal resisting elements (diaphragms)
iii) All of the above
iv) None of the above
Choose Correct
24 Horizontal Irregularities result in
i) Torsion
ii) Diaphragm deformation
iii) Stress Concentration
iv) All of the above
v) None of the above
Choose Correct
25 Vertical Irregularities are
i) Sudden change of stiffness over height of building
ii) Sudden change of strength over height of building
iii) Sudden change of geometry over height of building
iv) Sudden change of mass over height of building
v) All of the above
vi) None of the above
Choose Correct
26 Soft story in one
i) Which has lateral stiffness lt 70 of story above
ii) Which has lateral stiffness lt 80 of average lateral stiffness of 3
storeys above
iii)All of the above
vi) None of the above
Choose Correct
27 Extreme soft storey in one
i) Which has lateral stiffness lt 60 of storey above
ii) Which has lateral stiffness lt 70 of average lateral stiffness of 3
storeys above
iii)All of the above
iv)None of the above
Choose Correct
28 Weak Storey is one
i) Which has lateral strength lt 80 of storey above
ii) Which has lateral strength lt 80 of storey above
iii)All of the above
iv)None of the above
Choose Correct
29 Natural Period of Building
It is the time taken by the building to undergo one complete
cycle of oscillation during shaking
True False
30 Fundamental Natural Period of Building
Natural period with smallest Natural Frequency ie with largest
natural period is called Fundamental Natural Period
True False
31
Type of building frame system
i) Ordinary RC Moment Resisting Frame (OMRF)
ii) Special RC Moment Resisting Frame (SMRF)
iii) Ordinary Shear Wall with OMRF
iv) Ordinary Shear Wall with SMRF
v) Ductile Shear wall with OMRF
vi) Ductile Shear wall with SMRF
vii) All of the above
Choose Correct
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32 Zone factor to be considered for
i) Zone II ndash 010
ii) Zone III ndash 016
iii) Zone IV ndash 024
iv) Zone V ndash 036
True False
33 Importance Factor
i) Important building like school hospital railway station 15
ii) All other buildings 10
True False
34 Design of Earthquake effect is termed as
i) Earthquake Proof Design
or
ii) Earthquake Resistant Design
Choose Correct
35 Seismic Analysis is carried out by
i) Dynamic analysis procedure [Clause 78 of IS1893 (Part I) 2002]
ii) Simplified method referred as Lateral Force Procedure [Clause
75 of IS 1893 (Part I) 2002]
True False
36 Dynamic Analysis is performed for following buildings
(a) Regular Building gt 40 m height in Zone IV amp V
gt 90 height in Zone II amp III
(b) Irregular Building
gt 12 m all framed building in Zone IV amp V
gt 40 m all framed building in Zone II and III
True False
37 Base Shear for Lateral Force Procedure is
VB = Ah W =
True False
38 Distribution of Base Shear to different Floor level is
True False
39 Concept of capacity design is to
Ensure that brittle element will remain elastic at all loads prior to
failure of ductile element
True False
40 lsquoStrong Column ndash Weak Beamrsquo Philosophy is
For a building to remain safe during Earthquake shacking columns
should be stronger than beams and foundation should be stronger
than columns
True False
41 Rigid Diaphragm Action is
Geometric distortion of Slab in horizontal plane under influence of
horizontal Earthquake force is negligible This behaviour is known
as Rigid Diaphragm Action
True False
42 Soft storied buildings are
Column on Ground Storey do not have infill walls (of either
masonry or RC)
True False
43 Soft Storey or Open Ground Story is also termed as weak storey True False
44 Short columns in building suffer significant damage during an earth-
quake
True False
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45 Building can be protected from damage due to Earthquake effect by
using
a) Base Isolation Devices
b) Seismic Dampers
True False
46 Idea behind Base Isolation is
To detach building from Ground so that EQ motion are not
transmitted through the building or at least greatly reduced
True False
47 Base Isolation is done through
Flexible Pads connected to building and foundation True False
48 Seismic Dampers are
(i) Special devices to absorb the energy provided by Ground Motion
to the building
(ii) They act like hydraulic shock absorber in cars
True False
49 Commonly used Seismic Dampers are
(i) Viscous Dampers
(ii) Friction Dampers
(iii) Yielding Dampers
True False
50 For Ductility Requirement
(i) Min Grade of Concrete shall be M20 for all buildings having
more than 3 storeys in height
(ii) Steel Reinforcement of Grade Fe 415 or less only shall be used
(iii) Grade Fe 500 amp Fe 550 having elongation more than 145 may
be used
True False
51 For Ductility Requirement Flexure Members shall satisfy the
following requirement
(i) width of member shall not be less than 200 mm
(ii) width to depth ratio gt 03
(iii) depth of member D lt 14th of clear span
(iv) Factored Axial Stress on the member under Earthquake loading
shall not be greater than 01 fck
True False
52 For Ductility Requirement Longitudinal reinforcement in Flexure
Member shall satisfy the following requirements
i) Top and bottom reinforcement consist of at least 2 bars
throughout member length
ii) Tensile Steel Ratio on any face at any section shall not be less
than ρmin = (024 radic fck) fy
iii) Max Steel ratio on any face at any section shall not exceed
ρmax = 0025
iv) + ve steel at Joint face must be at least equal to half the ndashve steel
at that face
v) Steel provided at each of the top amp bottom face of the member
at any section along its length shall be at least equal to 14th of
max ndashve moment steel provided at the face of either joint
True False
कमटक2017नसईआरबी10
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151
(vi) Detailing of Reinforcement at Beam-Column Joint
(vii) Detailing of Splicing
53 For Ductile Requirement in compression member
i) Minimum diversion of member shall not be less than 200 mm
ii) In Frames with beams cc Span gt 5m or
unsupported length of column gt 4 m shortest dimension shall not
be less than 300 mm
iii) Ratio of shortest cross sectional dimension to the perpendicular
dimension shall probably not less than 04
True False
54 For Ductile Requirement Longitudinal reinforcement in compression
member shall satisfy the following requirements
i) Lap splice shall be provided only in the central half of the member
length proportional as tension splice
ii) Hoop shall be provided over entire splice length at spacing not
greater than 150 mm
iii) Not more than 50 bar shall be spliced at one section
True False
55 When a column terminates into a footing or mat special confining
reinforcement shall extend at least 300 mm into the footing or mat
True False
कमटक2017नसईआरबी10
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152
सोदभयगरोथ सची BIBLIOGRAPHY
1 Guidelines for Earthquake Resistant Non-Engineered Construction reprinted by
Indian Institute of Technology Kanpur 208016 India (Source wwwniceeorg)
2 IS 1893 (Part 1) 2002 Criteria for Earthquake Resistant Design Of Structures
PART- 1 GENERAL PROVISIONS AND BUILDINGS (Fifth Revision )
3
IS 4326 1993 (Reaffirmed 1998) Edition 32 (2002-04) Earthquake Resistant
Design and Construction of Buildings ndash Code of Practice ( Second Revision )
(Incorporating Amendment Nos 1 amp 2)
4 IS 13828 1993 (Reaffirmed 1998) Improving Earthquake Resistance of Low
Strength Masonry Buildings ndash Guidelines
5
IS 13920 1993 (Reaffirmed 1998) Edition 12 (2002-03) Ductile Detailing of
Reinforced Concrete Structures subjected to Seismic Forces ndash Code of Practice
(Incorporating Amendment Nos 1 amp 2)
6 IS 13935 1993 (Reaffirmed 1998) Edition 11 (2002-04) Repair and Seismic
Strengthening of Buildings ndash Guidelines (Incorporating Amendment No 1)
7
Earthquake Tips authored by Prof C V R Murty IIT Kanpur and sponsored by
Building Materials and Technology Promotion Council New Delhi India
(Source www wwwiitkacin)
8
Earthquake Engineering Practice Volume 1 Issue 1 March 2007 published by
National Information Center of Earthquake Engineering IIT Kanpur Kanpur
208016
9 Earthquake Resistant Design of Structures by Pankaj Agarwal and Manish
Shrikhande published by PHI Learning Private Limited Delhi 110092 (2015)
कमटक2017नसईआरबी10
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153
तटपपणी NOTES
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154
तटपपणी NOTES
कमटक2017नसईआरबी10
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155
हमारा उददशय
अनरकषि परौधौधगकी और कायापरिाली को उननयन करना तथा उतपादकता और
रलव की पररसमपवियो एव िनशजतत क ननषपादन म सधार करना जिसस
अतववाियो म ववशवसनीयता उपयोधगता और दकषता परापत की िा सकA
Our Objective
To upgrade Maintenance Technologies and Methodologies and achieve
improvement in productivity and performance of all Railway assets and
manpower which inter-alia would cover Reliability Availability and
Utilisation
तिसलमर Disclaimer
The document prepared by CAMTECH is meant for the dissemination of the knowledge information
mentioned herein to the field staff of Indian Railways The contents of this handbookbooklet are only for
guidance Most of the data amp information contained herein in the form of numerical values are indicative
and based on codes and teststrials conducted by various agencies generally believed to be reliable While
reasonable care and effort has been taken to ensure that information given is at the time believed to be fare
and correct and opinion based thereupon are reasonable Due to very nature of research it can not be
represented that it is accurate or complete and it should not be relied upon as such The readeruser is
supposed to refer the relevant codes manuals available on the subject before actual implementation in the
field
कमटक2017नसईआरबी10
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156
Hkkjrh jsy jkrdquoV ordf dh thou js[kk ---hellip
INDIAN RAILWAYS Lifeline to the nation hellip
If you have any suggestion amp comments please write to us
Contact person Joint Director (Civil)
Phone (0751) - 2470869
Fax (0751) ndash 2470841
Email dircivilcamtechgmailcom
Charbagh Railway Station Lucknow
FOREWORD
It is very heartening to know that a Handbook on Construction of
Earthquake Resistant Buildings is being brought out by CAMTECH Directorate
Gwalior under the aegis of RDSO The complex theory and practical issues
related to Earthquake magnitude its measurement earthquake resistant design
preferred building layout and design based on Earthquake spectrum analysis has been
presented in a lucid and informative manner for adoption in the field by Civil
Engineers Solvedmiddot examples have also been included illustrating calculation of design
forces in structural member for multi-storied building Provisions
contained in Seismic Code IS 1893 amp others have been brought out related to
building layout seismic forces calculation and reinforcement detailing
Details of retro-fitment for buildings have been also included which can
adopted by serving Engineers to make buildings Earthquake Resistant in an
effective and economical manner
I congratulate ADG and EDWorks of RDSO for editing amp Civil Engineers
of CAMTECH for compilation of very informative Handbook
New Delhi 20
th July 2017
vkfnR dqekj feRry AK MITTAL
F o r e w o r d
It is indeed very heartening to know that CAMTECH under the direction from RDSO has brought out a Handbook on ldquoConstruction of Earthquake Resistant Buildingsrdquo
It is also worth mentioning that on IR there were no comprehensive Guidelines or instructions regarding construction of Earthquake Resistant Buildings This handbook shall bridge the gap amp provide technical information on Earthquake phenomenon assessment of magnitude of earthquake general principles for earthquake resistance in Building-layout dynamic response of Buildings
Codal based procedure for determining lateral earthquake forces with special
reference to lsquoDuctility amp Capacity Design Conceptsrsquo has been brought out Solved examples illustrate calculation of design forces for structural members of multi-storied building Provisions contained in Seismic Code IS 1893 amp others have been brought out related to buildings which shall help structural designers and project engineers Chapter on Seismic Evaluation and Retrofitting gives in-sight to serving Engineers in the field to assess building for earthquake resistance and action required thereof in economical manner Thanks are due to Dr SK Thakkar Professor (Retd) IITRoorkee for technical review of this Handbook I congratulate Works amp Bridge Dte of RDSO for editing and Sh DK Gupta Jt Director Civil of CAMTECH involved in compilation of this Handbook for their praise worthy efforts
(J S Sondhi) Addl Director General
RDSO Dt 20072017
पराककथन
दनिया क कई निससो म िाल िी म आए भको पसो ि इमारतसो और जीवि कस काफी िकसाि पहोचाया ि भको प की दनि स दखा जाए तस सबस खतरिाक भवि निमााण
unreinforced ईोट या concrete बलॉक का िसता ि चार मोनजलसो तक क अनिकाोश घरसो कस परबनलत को करीट सलब क साथ burnt clay ईोट नचिाई स निनमात नकया जा रिा ि इसी तरि कई िए चार या पाोच मोनजला घर जस नक छसट और बड शिरसो म परबनलत को करीट फरम स बिाए गए ि म एक उनचत फरम परणाली की कमी रिती ि
िाल िी म आए भको पसो क कारण भारत म इमारतसो और घरसो कस कस सरनित रखा जाय इस पर परमखता स चचाा हई ि भको पीय दशसो म इोजीनियसा कस यि मितवपणा नजममदारी सनिनित करिा ि नक िए निमााण भको प परनतरसिी िसो और यि भी नक उनह मौजदा कमजसर सोरचिाओो दवारा उतपनन समसया का समािाि भी निकालिा ि
यि आशा की जाती ि नक कमटक दवारा तयार पसतिका नसनवल सोरचिाओो क निमााण एवो रखरखाव की गनतनवनियसो म लग भारतीय रलव क इोजीनियररोग कनमायसो क नलए काफी मददगार िसगी
कमटक गवातलयर (ए आर िप) 23 मई 2017 काययकारी तनदशक
FOREWORD
The recent earthquakes occurred in many parts of world has caused considerable damage
to the buildings and lives The most dangerous building construction from an
earthquake point of view is unreinforced brick or concrete block Most houses of upto
four storeys are built of burnt clay brick masonry with reinforced concrete slabs
Similarly many new four or five storey reinforced concrete frame building being
constructed in small and large towns lack a proper frame system
With the recent earthquakes the discussion on how safe buildings and houses are in
India has gained prominence Engineers in seismic countries have the important
responsibility to ensure that the new construction is earthquake resistant and also they
must solve the problem posed by existing weak structures
It is expected that the handbook prepared by CAMTECH will be quite helpful to the
engineering personnel of Indian Railways engaged in construction and maintenance
activities of civil structures
CAMTECHGwalior (AR Tupe)
23 May 2017 Executive Director
भतमका
भारतीय रलव एक बड़ा सगठन ह जिसक पास ससववल इिीननयररग सरचनाओ एव भवनो की ववशाल सपदा मौिद ह भकप की ववनाशकारी परकनत को धयान म रखत हए यह आवशयक ह कक लगभग सभी भवनो चाह व आवासीय ससथागत शकषणिक इतयादद क हो उनकी योिना डििाइन ननमााि तथा रखरखाव भकप परनतरोधी तरीको को अपनाकर ककया िाना चादहए जिसस कक भकप क कारि मानव िीवन व सपवि क नकसान को नयनतम ककया िा सक
ldquoभकप परतिरोधी भवनो क तनरमाणrdquo पर यह हसतपजसतका एक िगह पर पयाापत सामगरी परदान करन का एक परयास ह ताकक वयजतत भवनो क भकप परनतरोधी ननमााि क सलए मलभत ससदधातो को ववकससत कर सही तथा वयवहाररक कायाववधध को अमल म ला सक
इस हसतपजसतका की सामगरी को गयारह अधयायो म ववभाजित ककया गया ह अधयमय-1 पररचय तथा अधयमय-2 भकप इिीननयररग म परयतत शबदावली पररभावित करता ह अधयमय-3 भकप व भकपी खतरो क बार म बननयादी जञान को सकषप म वणिात करता ह अधयमय- 4 भकप पररमाि तथा तीवरता क माप क साथ भारत क भकपीय ज़ोन मानधचतर भकप की ननगरानी क सलए एिससयो क बार म िानकारी परदान करता ह अधयमय-5 व 6 भवन लआउट म भकप परनतरोध क सधार क सलए वयापक ससदधात को बताता ह अधयमय-7 भवन की गनतशील परनतकिया को दशााता ह अधयमय-8 और 9 म कोि पर आधाररत पाशवा बल ननधाारि का तरीका तथा बहमजिला भवन की ldquoितटाइल डिटसलग तथा कपससटी डििाइनrdquo को धयान म रखत हए डििाइन का उदाहरि परसतत ककया गया ह अधयमय-10 म कम शजतत की धचनाई दवारा सरचनाओ क ननमााि को भकप परनतरोधी ससदधातो को धयान म रख वणिात ककया गया ह अधयमय -11 म मौिदा भवनो की भकप परनतरोधी आवशयकताओ को परा करन क सलए भवनो क मौिदा भकपरोधी मलयाकन और पनः सयोिन पर परकाश िाला गया ह
यह हसतपजसतका मखयतः भारतीय रल क फीलि तथा डििाइन कायाालय म कायारत िईएसएसई सतर क सलए ह इस हसतपजसतका को भारतीय रल क ससववल इिीननयसा तथा अनय ववभागो क इिीननयसा दवारा एक सदभा पजसतका क रप म भी इसतमाल ककया िा सकता ह
म शरी एस क ठतकर परोफसर (ररटायिा) आई आई टी रड़की को उनक दवारा ददय गए मागादशान तथा सझावो क सलए अतयनत आभारी ह तथा शरी क सी शातय एसएसईससववल को इस हसतपजसतका क सकलन म उनक समवपात सहयोग क सलए धनयवाद दता ह
यदयवप इस हसतपजसतका को तयार करन म हर तरह की सावधानी बरती गई ह कफर भी कोई तरदट या चक हो तो कपया IRCAMTECHGwalior की िानकारी म लायी िा सकती ह
भारतीय रल क सभी अधधकाररयो और इकाइयो दवारा पसतक की सामगरी म ववसतार तथा सधार क सलए ददय िान वाल सझावो का सवागत ह
कमटक गवातलयर (िी क गपता) 23 मई 2017 सोयकत तनदशकतसतवल
PREFACE
Indian Railways is a big organisation having large assets of Civil Engineering Structures
and Buildings Keeping in mind the destructive nature of Earthquake it is essential that
almost all buildings whether residential institutional educational assembly etc should
be planned designed constructed as well as maintained by adopting Earthquake
Resistant features so that loss due to earthquake to human lives and properties can be
minimised
This handbook on ldquoConstruction of Earthquake Resistant Buildingsrdquo is an attempt to
provide enough material at one place for individual to develop the basic concept for
correctly interpreting and using practices for earthquake resistant construction of
Buildings
Content of this handbook is divided into Eleven Chapters Chapter-1 is Introduction
and Chapter-2 defines Terminology frequently used in Earthquake Engineering
Chapter-3 describes in brief Basic knowledge about Earthquake amp Seismic Hazards
Chapter-4 deals with Measurement of Earthquake magnitude amp intensity with
information about Seismic Zoning Map of India and Agencies for Earthquake
monitoring Chapter-5 amp 6 elaborates General Principle for improving Earthquake
resistance in building layouts Chapter-7 features Dynamic Response of Building In
Chapter-8 amp 9 Codal based procedure for determining lateral loads and Design of
multi-storeyed building with solved example considering Ductile Detailing and Capacity
Design Concept is covered Chapter-10 describes Construction of Low strength
Masonry Structure considering earthquake resistant aspect Chapter-11 enlighten
ldquoSeismic Evaluation amp Retrofittingrdquo for structural upgrading of existing buildings to
meet the seismic requirements
This handbook is primarily written for JESSE level over Indian Railways working in
Field and Design office This handbook can also be used as a reference book by Civil
Engineers and Engineers of other departments of Indian Railways
I sincerely acknowledge the valuable guidance amp suggestion by Shri SK Thakkar
Professor (Retd) IIT Roorkee and also thankful to Shri KC Shakya SSECivil for his
dedicated cooperation in compilation of this handbook
Though every care has been taken in preparing this handbook any error or omission
may please be brought out to the notice of IRCAMTECHGwalior
Suggestion for addition and improvement in the contents from all officers amp units of
Indian Railways are most welcome
CAMTECHGwalior (DK Gupta)
23 May 2017 Joint DirectorCivil
तवषय-सची CONTENT
अधयाय CHAPTER
तववरण DESCRIPTION
पषठ
सोPAGE
NO
पराककथन FOREWORD FROM MEMBER ENGINEERING RLY BOARD पराककथन FOREWORD FROM ADG RDSO पराककथन FOREWORD FROM ED CAMTECH भतमका PREFACE
तवषय-सची CONTENT
सोशोधन पतचययाो CORRECTION SLIPS
1 पररचय Introduction 01
2 भको प इोजीतनयररोग क तलए शबदावली Terminology for Earthquake
Engineering 02-05
3 भको प क बार म About Earthquake 06-16
31 भको प Earthquake 06
32 नकि कारणसो स िसता ि भको प What causes Earthquake 06
33 नववतानिक गनतनवनि Tectonic Activity 06
34 नववतानिक पलट का नसदाोत Theory of Plate Tectonics 07
35 लचीला ररबाउोड नसदाोत Elastic Rebound Theory 11
36 भको प और दसष क परकार Types of Earthquakes and Faults 11
37 जमीि कस निलती ि How the Ground shakes 12
38 भको प या भको पी खतरसो का परभाव Effects of Earthquake or Seismic
Hazards 13
4 भको पी जोन और भको प का मापन Seismic Zone and Measurement
of Earthquake 17-28
41 भको पी जसि Seismic Zone 17
42 भको प का मापि Measurement of Earthquake 19
43 भको प पररमाण सकल क परकार Types of Earthquake Magnitude
Scales 20
44 भको प तीवरता Earthquake Intensity 22
45 भको प निगरािी और सवाओो क नलए एजनसयसो Agencies for Earthquake
Monitoring and Services 28
5 भवन म भको प परतिरोध म सधार क तलए सामानय तसदाोि General
Principle for improving Earthquake Resistance in Building 29-33
51 िलकापि Lightness 29
52 निमााण की निरोतरता Continuity of Construction 29
53 परसजसतटोग एवो ससपडड पाटटास Projecting and Suspended Parts 29
54 भवि की आकनत Shape of Building 29
55 सनविा जिक नबसतडोग लआउट Preferred Building Layouts 30
56 नवनभनन नदशाओो म शसति Strength in Various Directions 30
57 िी ोव Foundations 30
58 छत एवो मोनजल Roofs and Floors 30
59 सीनियाो Staircases 31
510 बॉकस परकार निमााण Box Type Construction 33
511 अनि सरिा Fire Safety 33
6
भको प क दौरान आर सी भवनो ो क परदशयन पर सटरकचरल अतनयतमििाओो
का परभाव Effect of Structural Irregularities on Performance of
RC Buildings during Earthquakes
34-38
61 सटर कचरल अनियनमतताओो का परभाव Effect of Structural Irregularities 34
62 िनतज अनियनमतताएो Horizontal Irregularities 34
63 ऊरधाािर अनियनमतताएो Vertical Irregularities 36
64
भवि नवनयास अनियनमतताएो ndash समसयाए ववशलिि एव ननदान क उपाय Building Irregularities ndash Problems Analysis and Remedial
Measures 37
7 भवन की िायनातमक तवशषिाएा Dynamic Characteristics of
Building 39-47
71 डायिानमक नवशषताए Dynamic Characteristics 39
72 पराकनतक अवनि Natural Period 39
73 पराकनतक आवनि Natural Frequency 39
74 पराकनतक अवनि कस परभानवत करि वाल कारक Factors influencing
Natural Period 40
75 Mode आकनत Mode Shape 42
76 Mode आकनतयसो कस परभानवत करि वाल कारक Factors influencing
Mode Shapes 44
77 सोरचिा की परनतनकरया Response of Structure 46
78 नडजाइि सपटर म Design Spectrum 46
8 तिजाइन पारशय बलो ो क तनधायरण क तलए कोि आधाररि िरीका Code
Based Procedure for Determination of Design Lateral Loads 48-59
81 भको पी नडजाइि की नफलससफ़ी Philosophy of Seismic Design 48
82 भको पी नवशलषण क नलए तरीक Methods for Seismic Analysis 48
83 डायिानमक नवशलषण Dynamic Analysis 49
84 पारशा बल परनकरया Lateral Force Procedure 49
85 को पि की मौनलक पराकनतक अवनि Fundamental Natural Period of
Vibration 52
86 नडजाइि पारशा बल Design Lateral Force 53
87 नडजाइि बल का नवतरण Distribution of Design Force 53
88 नडजाइि उदािरण Design Example ndash To determine Base Shear and
its distribution along Height of Building 54
9 ढााचागि सोरचना का तनमायण Construction of Framed Structure 60-90
91
गरतवाकषाण लसनडोग और भको प लसनडोग म आर सी नबसतडोग का वयविार Behaviour of RC Building in Gravity Loading and Earthquake
Loading 60
92 परबनलत को करीट इमारतसो पर िनतज भको प का परभाव Effect of Horizontal
Earthquake Force on RC Buildings 61
93 िमता नडजाइि सोकलपिा Capacity Design Concept 61
94 लचीलापि और ऊजाा का अपवयय Ductility and Energy Dissipation 62
95 lsquoमजबतिोभ ndash कमजसर बीमrsquo फलससफ़ी lsquoStrong Column ndash Weak
Beamrsquo Philosophy 62
96 कठसर डायाफराम नकरया Rigid Diaphragm Action 63
97
सॉफट सटसरी नबसतडोग क साथ ndash ओपि गराउोड सटसरी नबसतडोग जस नक भको प क
समय कमजसर िसती ि Building with Soft storey ndash Open Ground
Storey Building that is vulnerable in Earthquake 63
98 भको प क दौराि लघ कॉलम वाली इमारतसो का वयविार Behavior of
Buildings with Short Columns during Earthquakes 65
99 भको प परनतरसिी इमारतसो की लचीलापि आवशयकताए Ductility
requirements of Earthquake Resistant Buildings 66
910
बीम नजनह आर सी इमारतसो म भको प बलसो का नवरसि करि क नलए डाला जाता
ि Beams that are required to resist Earthquake Forces in RC
Buildings 66
911 फलकसचरल ममबसा क नलए सामानय आवशयकताए General Requirements
for Flexural Members 68
912
कॉलम नजनह आर सी इमारतसो म भको प बलसो का नवरसि करि क नलए डाला
जाता ि Columns that are required to resist Earthquake Forces in
RC Buildings 69
913 एकसीयल लसडड मबसा क नलए सामानय आवशयकताए General
Requirements for Axial Loaded Members 71
914 बीम-कॉलम जसड जस आर सी भविसो म भको प बलसो का नवरसि करत ि Beam-
Column Joints that resist Earthquakes Forces in RC Buildings 72
915 नवशष सीनमत सदढीकरण Special Confining Reinforcement 74
916
नवशषतः भको पीय ितर म कतरिी दीवारसो वाली इमारतसो का निमााण Construction of Buildings with Shear Walls preferably in Seismic
Regions 75
917 इमपरवड नडजाइि रणिीनतयाो Improved design strategies 76
918 नडजाइि उदािरण Design Example ndash Beam Design of RC Frame
with Ductile Detailing 78
10 अलप सामरथय तचनाई सोरचनाओो क तनमायण Construction of Low
Strength Masonry Structures 91-106
101 भको प क दौराि ईोट नचिाई की दीवारसो का वयविार Behaviour of
Brick Masonry Walls during Earthquakes 91
102 नचिाई वाली इमारतसो म बॉकस एकशि कस सनिनित कर How to ensure
Box Action in Masonry Buildings 92
103 िनतज बड की भनमका Role of Horizontal Bands 93
104 अिसलोब सदढीकरण Vertical Reinforcement 95
105 दीवारसो म सराखसो का सोरिण Protection of Openings in Walls 96
106
भको प परनतरसिी ईोट नचिाई भवि क निमााण ित सामानय नसदाोत General
Principles for Construction of Earthquake Resistant Brick
Masonry Building
97
107 ओपनिोग का परभाव Influence of Openings 100
108 िारक दीवारसो म ओपनिोग परदाि करि की सामानय आवशयकताए General Requirements of Providing Openings in Bearing Walls
100
109 भको पी सदिीकरण वयवसथा Seismic Strengthening Arrangements 101
1010 भको प क दौराि सटसि नचिाई की दीवारसो का वयविार Behaviour of Stone
Masonry Walls during Earthquakes 104
1011
भकप परनतरोधी सटोन धचनाई क ननमााि हत सामानय ससदधात General
Principles for Construction of Earthquake Resistant Stone
Masonry Building
104
11 भकपीय रलयमकन और रटरोफिट ग Seismic Evaluation and
Retrofitting 107-142
111 भकपीय मलयाकन Seismic Evaluation 107
112 भवनो की रटरोकिदटग Retrofitting of Building 116
113
आरसी भवनो क घटको म सामानय भकपी कषनतया और उनक उपचार Common seismic damage in components of RC
Buildings and their remedies 133
114 धचनाई सरचनाओ की रटरोकिदटग Retrofitting of Masonry
Structures 141
Annex ndash I भारिीय भको पी सोतििाएा Indian Seismic Codes 143-145
Annex ndash II Checklist Multiple Choice Questions for Points to be kept in
mind during Construction of Earthquake Resistant Building 146-151
सोदभयगरोथ सची BIBLIOGRAPHY 152
तटपपणी NOTES 153-154
हमारा उददशय एव डिसकलरर OUR OBJECTIVE AND DISCLAIMER
सोशसिि पनचायसो का परकाशि
ISSUE OF CORRECTION SLIPS
इस ििपसतिका क नलए भनवषय म परकानशत िसि वाली सोशसिि पनचायसो कस निमनािसार सोखाोनकत
नकया जाएगा
The correction slips to be issued in future for this handbook will be numbered as
follows
कमटक2017नसईआरबी10सीएस XX नदिाोक_____________________
CAMTECH2017CERB10CS XX date_________________________
जिा xx सोबसतित सोशसिि पची की करम सोखा ि (01 स परारमभ िसकर आग की ओर)
Where ldquoXXrdquo is the serial number of the concerned correction slip (starting
from 01 onwards)
परकातशि सोशोधन पतचययाा W a
CORRECTION SLIPS ISSUED
करसो Sr No
परकाशन
तदनाोक Date of
issue
सोशोतधि पषठ सोखया िथा मद सोखया Page no and Item No modified
तटपपणी Remarks
कमटक2017नसईआरबी10
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भकमप परनतरसिी भवि निमााण मई ndash 2017 CONSTRUCTION OF EARTHQUAKE RESISTANT BUILDING May ndash 2017
1
अधयाय Chapter ndash 1
पररचय Introduction
To avoid a great earthquake disaster with its severe consequences special consideration must be
given Engineers in seismic countries have the important responsibility to ensure that the new
construction is earthquake resistant and also they must solve the problem posed by existing weak
structures
Most of the loss of life in past earthquakes has occurred due to the collapse of buildings
constructed with traditional materials like stone brick adobe (kachcha house) and wood which
were not particularly engineered to be earthquake resistant In view of the continued use of such
buildings it is essential to introduce earthquake resistance features in their construction
The problem of earthquake engineering can be divided into two parts first to design new
structures to perform satisfactorily during an earthquake and second to retrofit existing structures
so as to reduce the loss of life during an earthquake Every city in the world has a significant
proportion of existing unsafe buildings which will produce a disaster in the event of a strong
ground shaking Engineers have the responsibility to develop appropriate methods of retrofit
which can be applied when the occasion arises
The design of new building to withstand ground shaking is prime responsibility of engineers and
much progress has been made during the past 40 years Many advances have been made such as
the design of ductile reinforced concrete members Methods of base isolation and methods of
increasing the damping in structures are now being utilized for important buildings both new and
existing Improvements in seismic design are continuing to be made such as permitting safe
inelastic deformations in the event of very strong ground shaking
A problem that the engineer must share with the seismologistgeologist is that of prediction of
future occurrence of earthquake which is not possible in current scenario
Earthquake resistant construction requires seismic considerations at all stages from architectural
planning to structural design to actual constructions and quality control
Problems pertaining to Earthquake engineering in a seismic country cannot be solved in a short
time so engineers must be prepared to continue working to improve public safety during
earthquake In time they must control the performance of structures so that effect of earthquake
does not create panic in society and its after effects are easily restorable
To ensure seismic resistant construction earthquake engineering knowledge needs to spread to a
broad spectrum of professional engineers within the country rather than confining it to a few
organizations or individuals as if it were a super-speciality
कमटक2017नसईआरबी10
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2
अधयाय Chapter ndash 2
भको प इोजीतनयररोग क तलए शबदावली Terminology for Earthquake Engineering
21 फोकस या िाइपोसटर Focus or Hypocenter
In an earthquake the waves emanate from a finite area
of rocks However the point from which the waves
first emanate or where the fault movement starts is
called the earthquake focus or hypocenter
22 इपीसटर Epicentre
The point on the ground surface just above the focus is called the epicentre
23 सििी फोकस भको प Shallow Focus Earthquake
Shallow focus earthquake occurs where the focus is less than 70 km deep from ground surface
24 इोटरमीतिएट फोकस भको प Intermediate Focus Earthquake
Intermediate focus earthquake occurs where the focus is between 70 km to 300 km deep
25 गिरा फोकस भको प Deep Focus Earthquake
Deep focus earthquake occurs where the depth of focus is more than 300 km
26 इपीसटर दरी Epicentre Distance
Distance between epicentre and recording station in km or in degrees is called epicentre distance
27 पवय क झटक Foreshocks
Fore shocks are smaller earthquakes that precede the main earthquake
28 बाद क झटक Aftershocks
Aftershocks are smaller earthquakes that follow the main earthquake
29 पररमाण Magnitude
The magnitude of earthquake is a number which is a measure of energy released in an
earthquake It is defined as logarithm to the base 10 of the maximum trace amplitude expressed
in microns which the standard short-period torsion seismometer (with a period of 08s
Fig 21Basic terminology
कमटक2017नसईआरबी10
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3
magnification 2800 and damping nearly critical) would register due to the earthquake at an
epicentral distance of 100 km
210 िीवरिा Intensity
The intensity of an earthquake at a place is a measure of the strength of shaking during the
earthquake and is indicated by a number according to the modified Mercalli Scale or MSK
Scale of seismic intensities
211 पररमाण और िीवरिा क बीच बतनयादी फकय Basic difference between Magnitude and
Intensity
Magnitude of an earthquake is a measure of its size
whereas intensity is an indicator of the severity of
shaking generated at a given location Clearly the
severity of shaking is much higher near the
epicenter than farther away
This can be elaborated by considering the analogy
of an electric bulb Here the size of the bulb (100-
Watt) is like the magnitude of an earthquake (M)
and the illumination (measured in lumens) at a
location like the intensity of shaking at that location
(Fig 22)
212 दरवण Liquefaction
Liquefaction is a state in saturated cohesion-less soil wherein the effective shear strength is
reduced to negligible value for all engineering purpose due to pore pressure caused by vibrations
during an earthquake when they approach the total confining pressure In this condition the soil
tends to behave like a fluid mass
213 तववियतनक लकषण Tectonic Feature
The nature of geological formation of the bedrock in the earthrsquos crust revealing regions
characterized by structural features such as dislocation distortion faults folding thrusts
volcanoes with their age of formation which are directly involved in the earth movement or
quake resulting in the above consequences
214 भको पी दरवयमान Seismic Mass
It is the seismic weight divided by acceleration due to gravity
215 भको पी भार Seismic Weight
It is the total dead load plus appropriate amounts of specified imposed load
Fig 22 Reducing illumination with distance
from an electric bulb
कमटक2017नसईआरबी10
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4
216 आधार Base
It is the level at which inertia forces generated in the structure are transferred to the foundation
which then transfers these forces to the ground
217 दरवयमान का क दर Centre of Mass
The point through which the resultant of the masses of a system acts is called Centre of Mass
This point corresponds to the centre of gravity of masses of system
218 कठोरिा का क दर Centre of Stiffness
The point through which the resultant of the restoring forces of a system acts is called Centre of
stiffness
219 बॉकस परणाली Box System
Box is a bearing wall structure without a space frame where the horizontal forces are resisted by
the walls acting as shear walls
220 पटटा Band
A reinforced concrete reinforced brick or wooden runner provided horizontally in the walls to tie
them together and to impart horizontal bending strength in them
221 लचीलापन Ductility
Ductility of a structure or its members is the capacity to undergo large inelastic deformations
without significant loss of strength or stiffness
222 किरनी दीवार Shear Wall
Shear wall is a wall that is primarily designed to resist lateral forces in its own plane
223 िनय का बयौरा Ductile Detailing
Ductile Detailing is the preferred choice of location and amount of reinforcement in reinforced
concrete structures to provide adequate ductility In steel structures it is the design of members
and their connections to make them adequate ductile
224 लचीला भको पी तवरण गणाोक Elastic Seismic Acceleration Co-Efficient A
This is the horizontal acceleration value as a fraction of acceleration due to gravity versus
natural period of vibration T that shall be used in design of structures
कमटक2017नसईआरबी10
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225 पराकतिक अवतध Natural Period T
Natural period of a structure is its time period of undamped vibration
a) Fundamental Natural Period Tl It is the highest modal time period of vibration along the
considered direction of earthquake motion
b) Modal Natural Period Tk Modal natural period of mode k is the time period of vibration in
mode k
226 नॉमयल मोि Normal Mode
Mode of vibration at which all the masses in a structure attain maximum values of displacements
and rotations and also pass through equilibrium positions simultaneously
227 ओवरसटरगथ Overstrength
Strength considering all factors that may cause its increase eg steel strength being higher than
the specified characteristic strength effect of strain hardening in steel with large strains and
concrete strength being higher than specified characteristic value
228 ररसाोस कमी कारक Response Reduction Factor R
The factor by which the actual lateral force that would be generated if the structure were to
remain elastic during the most severe shaking that is likely at that site shall be reduced to obtain
the design lateral force
229 ररसाोस सकटर म Response Spectrum
The representation of the maximum response of idealized single degree freedom system having
certain period and damping during that earthquake The maximum response is plotted against the
undamped natural period and for various damping values and can be expressed in terms of
maximum absolute acceleration maximum relative velocity or maximum relative displacement
230 तमटटी परोफ़ाइल फकटर Soil Profile Factor S
A factor used to obtain the elastic acceleration spectrum depending on the soil profile below the
foundation of structure
कमटक2017नसईआरबी10
CAMTECH2017CERB10
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6
अधयाय Chapter ndash 3
भको प क बार म About Earthquake
31 भको प Earthquake
Vibrations of earthrsquos surface caused by waves coming from a source of disturbance inside the
earth are described as earthquakes
Earthquake is a natural phenomenon occurring with all uncertainties
During the earthquake ground motions occur in a random fashion both horizontally and
vertically in all directions radiating from epicentre
These cause structures to vibrate and induce inertia forces on them
32 तकन कारणो ो स िोिा ि भको प What causes Earthquake
Earthquakes may be caused by
Tectonic activity
Volcanic activity
Land-slides and rock-falls
Rock bursting in a mine
Nuclear explosions
33 तववियतनक गतितवतध Tectonic Activity
Tectonic activity pertains to geological formation of the bedrock in the earthrsquos crust characterized
by structural features such as dislocation distortion faults folding thrusts volcanoes directly
involved in the earth movement
As engineers we are interested in earthquakes that are large enough and close enough (to the
structure) to cause concern for structural safety- usually caused by tectonic activity
Earth (Fig 31) consists of following segments ndash
solid inner core (radius ~1290km) that consists of heavy
metals (eg nickel and iron)
liquid outer core(thickness ~2200km)
stiffer mantle(thickness ~2900km) that has ability to flow
and
crust(thickness ~5 to 40km) that consists of light
materials (eg basalts and granites)
At the Core the temperature is estimated to be ~2500degC the
pressure ~4 million atmospheres and density ~135 gmcc
this is in contrast to ~25degC 1 atmosphere and 15 gmcc on the surface of the Earth
Fig 31 Inside the Earth
कमटक2017नसईआरबी10
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7
Due to prevailing high temperature and pressure gradients between the Crust and the Core the
local convective currents in mantle (Fig 32) are developed These convection currents result in a
circulation of the earthrsquos mass hot molten lava comes out and the cold rock mass goes into the
Earth The mass absorbed eventually melts under high temperature and pressure and becomes a
part of the Mantle only to come out again from another location
Near the bottom of the crust horizontal component currents impose shear stresses on bottom of
crust causing movement of plates on earthrsquos surface The movement causes the plates to move
apart in some places and to converge in others
34 तववियतनक पलट का तसदाोि Theory of Plate Tectonics
Tectonic Plates Basic hypothesis of plate tectonics is that the earthrsquos surface consists of a
number of large intact blocks called plates or tectonic plates and these plates move with respect
to each other due to the convective flows of Mantle material which causes the Crust and some
portion of the Mantle to slide on the hot molten outer core The major plates are shown in
Fig 33
The earthrsquos crust is divided into six continental-sized plates (African American Antarctic
Australia-Indian Eurasian and Pacific) and about 14 of sub-continental size (eg Carribean
Cocos Nazca Philippine etc) Smaller platelets or micro-plates also have broken off from the
larger plates in the vicinity of many of the major plate boundaries
Fig 32 Convention current in mantle
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Fig 33 The major tectonic plates mid-oceanic ridges trenches and transform faults of
the earth Arrows indicate the directions of plate movement
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The relative deformation between plates occurs only in narrow zones near their boundaries
These deformations are
1 Aseismic deformation This deformation of the plates occurs slowly and continuously
2 Seismic deformation This deformation occurs with sudden outburst of energy in the form of
earthquakes
The boundaries are (i) Convergent (ii) Divergent (iii) Transform
Convergent boundary Sometimes the plate in the front is slower Then the plate behind it
comes and collides (and mountains are formed) This type of inter-plate interaction is the
convergent boundary (Fig 34)
Divergent boundary Sometimes two plates move away from one another (and rifts are
created) This type of inter-plate interaction is the divergent boundary (Fig 35)
Transform boundary Sometimes two plates move side-by-side along the same direction or in
opposite directions This type of inter-plate interaction is the transform boundary (Fig 36)
Since the deformation occurs predominantly at the boundaries between the plates it would be
expected that the locations of earthquakes would be concentrated near plate boundaries The map
of earthquake epicentres shown in Fig 37 provides strong support to confirm the theory of plate
tectonics The dots represent the epicentres of significant earthquakes It is apparent that the
locations of the great majority of earthquakes correspond to the boundaries between plates
Fig 34 Convergent Boundary
Fig 35 Divergent Boundary
Fig 36 Transform Boundary
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Fig 37 Worldwide seismic activity
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35 लचीला ररबाउोि तसदाोि Elastic Rebound Theory
Earth crust for some reason is moving in opposite
directions on certain faults This sets up elastic
strains in the rocks in the region near this fault As
the motion goes on the stresses build up in the
rocks until the stresses are large enough to cause
slip between the two adjoining portions of rocks
on either side A rupture takes place and the
strained rock rebounds back due to internal stress
Thus the strain energy in the rock is relieved
partly or fully (Fig 38)
Fault The interface between the plates where the movement has taken place is called fault
Slip When the rocky material along the interface of the plates in the Earthrsquos Crust reaches its
strength it fractures and a sudden movement called slip takes place
The sudden slip at the fault causes the earthquake A violent shaking of the Earth during
which large elastic strain energy released spreads out in the form of seismic waves that travel
through the body and along the surface of the
Earth
After elastic rebound there is a readjustment and
reapportion of the remaining strains in the region
The stress grows on a section of fault until slip
occurs again this causes yet another even though
smaller earthquake which is termed as aftershock
The aftershock activity continues until the
stresses are below the threshold level everywhere
in the rock
After the earthquake is over the process of strain build-up at this modified interface between the
tectonic plates starts all over again This is known as the Elastic Rebound Theory (Fig 39)
36 भको प और दोष क परकार Types of Earthquakes and Faults
Inter-plate Earthquakes Most earthquakes occurring along the boundaries of the tectonic
plates are called Inter-plate Earthquakes (eg 1897
Assam (India) earthquake)
Intra-plate Earthquakes Numbers of earthquakes
occurring within the plate itself but away from the
plate boundaries are called Intra-plate Earthquakes
(eg 1993 Latur (India) earthquake)
Note In both types of earthquakes the slip
generated at the fault during earthquakes is along
Fig 310 Type of Faults
Fig 38 Elastic Strain Build-Up and Brittle Rupture
Fig 39 Elastic Rebound Theory
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both vertical and horizontal directions (called Dip Slip) and lateral directions (called Strike
Slip) with one of them dominating sometimes (Fig 310)
37 जमीन कस तिलिी ि How the Ground shakes
Seismic waves Large strain energy released during an earthquake travels as seismic waves in all
directions through the Earthrsquos layers reflecting and refracting at each interface (Fig 311)
There are of two types of waves 1) Body Waves
2) Surface Waves
Body waves are of two types
a) Primary Waves (P-Wave)
b) Secondary Wave (S-Wave)
Surface waves are of two types namely
a) Love Waves
b) Rayleigh Waves
Body Waves Body waves have spherical wave front They consist of
Primary Waves (P-waves) Under P-waves [Fig 311(a)] material particles undergo
extensional and compressional strains along direction of energy transmission These waves
are faster than all other types of waves
Secondary Waves (S-waves) Under S-waves [Fig 311(b)] material particles oscillate at
Fig 311 Arrival of Seismic Waves at a Site
Fig 311(a) Motions caused by Primary Waves
Fig 311(b) Motions caused by Secondary Waves
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right angles to direction of energy transmission This type of wave shears the rock particle to
the direction of wave travel Since the liquid has no shearing resistance these waves cannot
pass through liquids
Surface Waves Surface waves have cylindrical wave front They consist of
Love Waves In case of Love waves [Fig 311(c)] the displacement is transverse with no
vertical or longitudinal components (ie similar to secondary waves with no vertical
component) Particle motion is restricted to near the surface Love waves being transverse
waves these cannot travel in liquids
Rayleigh Waves Rayleigh waves [Fig 311(d)] make a material particle oscillate in an
elliptic path in the vertical plane with horizontal motion along direction of energy
transmission
Note Primary waves are fastest followed in sequence by Secondary Love and Rayleigh waves
38 भको प या भको पी खिरो ो का परभाव Effects of Earthquake or Seismic Hazards
Basic causes of earthquake-induced damage are
Ground shaking
Structural hazards
Liquefaction
Ground failure Landslides
Tsunamis and
Fire
Fig 311(c) Motions caused by Love Waves
Fig 311(d) Motions caused by Rayleigh Waves
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381 जमीन को पन Ground shaking
Ground shaking can be considered to be the most important of all seismic hazards because all
the other hazards are caused by ground shaking
When an earthquake occurs seismic waves radiate away from the source and travel rapidly
through the earthrsquos crust
When these waves reach the ground surface they produce shaking that may last from seconds
to minutes
The strength and duration of shaking at a particular site depends on the size and location of
the earthquake and on the characteristics of the site
At sites near the source of a large earthquake ground shaking can cause tremendous damage
Where ground shaking levels are low the other seismic hazards may be low or nonexistent
Strong ground shaking can produce extensive damage from a variety of seismic hazards
depending upon the characteristics of the soil
The characteristics of the soil can greatly influence the nature of shaking at the ground
surface
Soil deposits tend to act as ldquofiltersrdquo to seismic waves by attenuating motion at certain
frequencies and amplifying it at others
Since soil conditions often vary dramatically over short distances levels of ground shaking
can vary significantly within a small area
One of the most important aspects of geotechnical earthquake engineering practice involves
evaluation of the effects of local soil conditions on strong ground motion
382 सोरचनातमक खिर Structural Hazards
Without doubt the most dramatic and memorable images of earthquake damage are those of
structural collapse which is the leading cause of death and economic loss in many
earthquakes
As the earth vibrates all buildings on the ground surface will respond to that vibration in
varying degrees
Earthquake induced accelerations velocities and displacements can damage or destroy a
building unless it has been designed and constructed or strengthened to be earthquake
resistant
The effect of ground shaking on buildings is a principal area of consideration in the design of
earthquake resistant buildings
Seismic design loads are extremely difficult to determine due to the random nature of
earthquake motions
Structures need not collapse to cause death and damage Falling objects such as brick facings
and parapets on the outside of a structure or heavy pictures and shelves within a structure
have caused casualties in many earthquakes Interior facilities such as piping lighting and
storage systems can also be damaged during earthquakes
However experiences from past strong earthquakes have shown that reasonable and prudent
practices can keep a building safe during an earthquake
Over the years considerable advancement in earthquake-resistant design has moved from an
emphasis on structural strength to emphases on both strength and ductility In current design
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practice the geotechnical earthquake engineer is often consulted for providing the structural
engineer with appropriate design ground motions
383 दरवीकरण Liquefaction
In some cases earthquake damage have occurred when soil deposits have lost their strength and
appeared to flow as fluids This phenomenon is termed as liquefaction In liquefaction the
strength of the soil is reduced often drastically to the point where it is unable to support
structures or remain stable Because it only occurs in saturated soils liquefaction is most
commonly observed near rives bays and other bodies of water
Soil liquefaction can occur in low density saturated sands of relatively uniform size The
phenomenon of liquefaction is particularly important for dams bridges underground pipelines
and buildings standing on such ground
384 जमीन तवफलिा लि सलाइि Ground Failure Land slides
1) Earthquake-induced ground Failure has been observed in the form of ground rupture along
the fault zone landslides settlement and soil liquefaction
2) Ground rupture along a fault zone may be very limited or may extend over hundreds of
kilometers
3) Ground displacement along the fault may be horizontal vertical or both and can be
measured in centimetres or even metres
4) A building directly astride such a rupture will be severely damaged or collapsed
5) Strong earthquakes often cause landslides
6) In a number of unfortunate cases earthquake-induced landslides have buried entire towns
and villages
7) Earthquake-induced landslides cause damage by destroying buildings or disrupting bridges
and other constructed facilities
8) Many earthquake-induced landslides result from liquefaction phenomenon
9) Others landslides simply represent the failures of slopes that were marginally stable under
static conditions
10) Landslide can destroy a building the settlement may only damage the building
385 सनामी Tsunamis
1) Tsunamis or seismic sea waves are generally produced by a sudden movement of the ocean
floor
2) Rapid vertical seafloor movements caused by fault rupture during earthquakes can produce
long-period sea waves ie Tsunamis
3) In the open sea tsunamis travel great distances at high speeds but are difficult to detect ndash
they usually have heights of less than 1 m and wavelengths (the distance between crests) of
several hundred kilometres
4) As a tsunami approaches shore the decreasing water depth causes its speed to decrease and
the height of the wave to increase
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5) As the water waves approach land their velocity decreases and their height increases from
5 to 8 m or even more
6) In some coastal areas the shape of the seafloor may amplify the wave producing a nearly
vertical wall of water that rushes far inland and causes devastating damage
7) Tsunamis can be devastating for buildings built in coastal areas
386 अति Fire
When the fire following an earthquake starts it becomes difficult to extinguish it since a strong
earthquake is accompanied by the loss of water supply and traffic jams Therefore the
earthquake damage increases with the earthquake-induced fire in addition to the damage to
buildings directly due to earthquakes
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अधयाय Chapter ndash 4
भको पी जोन और भको प का मापन Seismic Zone and Measurement of Earthquake
41 भको पी जोन Seismic Zone
Due to convective flow of mantle material crust of Earth and some portion of mantle slide on hot
molten outer core This sliding of Earthrsquos mass takes place in pieces called Tectonic Plates The
surface of the Earth consists of seven major tectonic plates (Fig 41)
They are
1 Eurasian Plate
2 Indo-Australian Plate
3 Pacific Plate
4 North American Plate
5 South American Plate
6 African Plate
7 Antarctic Plate
India lies at the northwestern end of the Indo Australian Plate (Fig 42) This Plate is colliding
against the huge Eurasian Plate and going under the Eurasian Plate Three chief tectonic sub-
regions of India are
the mighty Himalayas along the north
the plains of the Ganges and other rivers and
the peninsula
Most earthquakes occur along the Himalayan plate boundary (these are inter-plate earthquakes)
but a number of earthquakes have also occurred in the peninsular region (these are intra-plate
earthquakes)
Fig 41 Major Tectonic Plates on the Earthrsquos surface
Fig 42 Geographical Layout and Tectonic Plate
Boundaries in India
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Bureau of Indian Standards [IS1893 (part ndash 1) 2002] based on various scientific inputs from a
number of agencies including earthquake data supplied by Indian Meteorological Department
(IMD) has grouped the country into four seismic zones viz Zone II III IV and V Of these
Zone V is rated as the most seismically prone region while Zone II is the least (Fig 43)
Indian Seismic code (IS 18932002) divides the country into four seismic zones based on the
expected intensity of shaking in future earthquake The four zones correspond to areas that have
potential for shaking intensity on MSK scale as shown in the table
Seismic Zone Intensity on MSK scale of total area
II (Low intensity zone) VI (or less) 43
III (Moderate intensity zone) VII 27
IV (Severe intensity zone) VIII 18
V (Very Severe intensity zone) IX (and above) 12
Fig 43 Map showing Seismic Zones of India [IS 1893 (Part 1) 2002]
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42 भको प का मापन Measurement of Earthquake
421 मापन उपकरण Measuring Instruments
Seismograph The instrument that measures earthquake shaking is known as a seismograph
(Fig 44) It has three components ndash
Sensor ndash It consists of pendulum mass
string magnet and support
Recorder ndash It consists of drum pen and
chart paper
Timer ndash It consists of the motor that rotates
the drum at constant speed
Seismoscopes Some instruments that do not
have a timer device provide only the maximum
extent (or scope) of motion during the
earthquake
Digital instruments The digital instruments using modern computer technology records the
ground motion on the memory of the microprocessor that is in-built in the instrument
Note The analogue instruments have evolved over time but today digital instruments are more
commonly used
422 मापन क सकल Scale of Measurement
The Richter Magnitude Scale (also called Richter scale) assigns a magnitude number to quantify
the energy released by an earthquake Richter scale is a base 10 logarithmic scale which defines
magnitude as the logarithm of the ratio of the amplitude of the seismic wave to an arbitrary minor
amplitude
The magnitude M of an Earthquake is defined as
M = log10 A - log10 A0
Where
A = Recorded trace amplitude for that earthquake at a given distance as written by a
standard type of instrument (say Wood Anderson instrument)
A0 = Same as A but for a particular earthquake selected as standard
This number M is thus independent of distance between the epicentre and the station and is a
characteristic of the earthquake The standard shock has been defined such that it is low enough
to make the magnitude of most of the recorded earthquakes positive and is assigned a magnitude
of zero Thus if A = A0
Fig 44 Schematic of Early Seismograph
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M = log10 A0 - log10 A0 = 0
Standard shock of magnitude zero It is defined as one that records peak amplitude of one
thousandths of a millimetre at a distance of 100 km from the epicentre
1) Zero magnitude does not mean that there is no earthquake
2) Magnitude of an earthquake can be a negative number also
3) An earthquake that records peak amplitude of 1 mm on a standard seismograph at 100 km
will have its magnitude as
M = log10 (1) - log10 (10-3
)= 0 ndash (-3) = 3
Magnitude of a local earthquake It is defined as the logarithm to base 10 of the maximum
seismic wave amplitude (in thousandths of a mm) recorded on Wood Anderson seismograph at a
distance of 100 kms from the earthquake epicentre
1) With increase in magnitude by 10 the energy released by an earthquake increases by a
factor of about 316
2) A magnitude 80 earthquake releases about 316 times the energy released by a magnitude
70 earthquake or about 1000 times the energy released by a 60 earthquake
3) With increase in magnitude by 02 the energy released by the earthquake doubles
43 भको प पररमाण सकल क परकार Types of Earthquake Magnitude Scales
Several scales have historically been described as the ldquoRitcher Scalerdquo The Ritcher local
magnitude (ML) is the best known magnitude scale but it is not always the most appropriate scale
for description of earthquake size The Ritcher local magnitude does not distinguish between
different types of waves
At large epicentral distances body waves have usually been attenuated and scattered sufficiently
that the resulting motion is dominated by surface waves
Other magnitude scales that base the magnitude on the amplitude of a particular wave have been
developed They are
a) Surface Wave Magnitude (MS)
b) Body Wave Magnitude (Mb)
c) Moment Magnitude (Mw)
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431 सिि लिर पररमाण Surface Wave Magnitude (MS)
The surface wave magnitude (Gutenberg and Ritcher 1936) is a worldwide magnitude scale
based on the amplitude of Rayleigh waves with period of about 20 sec The surface wave
magnitude is obtained from
MS = log A + 166 log Δ + 20
Where A is the maximum ground displacement in micrometers and Δ is the epicentral distance of
the seismometer measured in degrees (3600 corresponding to the circumference of the earth)
The surface wave magnitude is most commonly used to describe the size of shallow (less than
about 70 km focal depth) distant (farther than about 1000 km) moderate to large earthquakes
432 बॉिी लिर पररमाण Body Wave Magnitude (Mb)
For deep-focus earthquakes surface waves are often too small to permit reliable evaluation of the
surface wave magnitude The body wave magnitude (Gutenberg 1945) is a worldwide magnitude
scale based on the amplitude of the first few cycles of p-waves which are not strongly influenced
by the focal depth (Bolt 1989) The body wave magnitude can be expressed as
Mb = log A ndash log T + 001Δ + 59
Where A is the p-wave amplitude in micrometers and T is the period of the p-wave (usually
about one sec)
Saturation
For strong earthquakes the measured
ground-shaking characteristics become
less sensitive to the size of the
earthquake than the smaller earthquakes
This phenomenon is referred to as
saturation (Fig 45)
The body wave and the Ritcher local
magnitudes saturate at magnitudes of 6
to 7 and the surface wave magnitude
saturates at about Ms = 8
To describe the size of a very large
earthquake a magnitude scale that does
not depend on ground-shaking levels
and consequently does not saturate
would be desirable
Fig 45 Saturation of various magnitude scale Mw (Moment
Magnitude) ML (Ritcher Local Magnitude) MS (Surface Wave
Magnitude) mb (Short-period Body Wave Magnitude) mB
(Long-period Body Wave Magnitude) and MJMA (Japanese
Meteorological Agency Magnitude)
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433 पल पररमाण Moment Magnitude (Mw)
The only magnitude scale that is not subject to saturation is the moment magnitude
The moment magnitude is given by
Mw = [(log M0)15] ndash 107
Where M0 is the seismic moment in dyne-cm
44 भको प िीवरिा Earthquake Intensity
Earthquake magnitude is simply a measure of the size of the earthquake reflecting the elastic
energy released by the earthquake It is usually referred by a certain real number on the Ritcher
scale (eg magnitude 65 earthquake)
On the other hand earthquake intensity indicates the extent of shaking experienced at a given
location due to a particular earthquake It is usually referred by a Roman numeral on the
Modified Mercalli Intensity (MMI) scale as given below
I Not felt except by a very few under especially favourable circumstances
II Felt by only a few persons at rest especially on upper floors of buildings delicately
suspended objects may swing
III Felt quite noticeably indoors especially on upper floors of buildings but many people
do not recognize it as an earthquake standing motor cars may rock slightly vibration
like passing of truck duration estimated
IV During the day felt indoors by many outdoors by few at night some awakened
dishes windows doors disturbed walls make cracking sound sensation like heavy
truck striking building standing motor cars rocked noticeably
V Felt by nearly everyone many awakened some dishes windows etc broken a few
instances of cracked plaster unstable objects overturned disturbances of trees piles
and other tall objects sometimes noticed pendulum clocks may stop
VI Felt by all many frightened and run outdoors some heavy furniture moved a few
instances of fallen plaster or damaged chimneys damage slight
VII Everybody runs outdoors damage negligible in buildings of good design and
construction slight to moderate in well-built ordinary structures considerable in
poorly built or badly designed structures some chimneys broken noticed by persons
driving motor cars
VIII Damage slight in specially designed structures considerable in ordinary substantial
buildings with partial collapse great in poorly built structures panel walls thrown out
of frame structures fall of chimneys factory stacks columns monuments walls
heavy furniture overturned sand and mud ejected in small amounts changes in well
water persons driving motor cars disturbed
IX Damage considerable in specially designed structures well-designed frame structures
thrown out of plumb great in substantial buildings with partial collapse buildings
shifted off foundations ground cracked conspicuously underground pipes broken
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X Some well-built wooden structures destroyed most masonry and frame structures
destroyed with foundations ground badly cracked rails bent landslides considerable
from river banks and steep slopes shifted sand and mud water splashed over banks
XI Few if any (masonry) structures remain standing bridges destroyed broad fissures in
ground underground pipelines completely out of service earth slumps and land slips
in soft ground rails bent greatly
XII Damage total practically all works of construction are damaged greatly or destroyed
waves seen on ground surface lines of sight and level are destroyed objects thrown
into air
441 MSK िीवरिा सकल MSK Intensity Scale
The MSK intensity scale is quite comparable to the Modified Mercalli intensity scale but is more
convenient for application in field and is widely used in India In assigning the MSK intensity
scale at a site due attention is paid to
Type of Structures (Table ndash A)
Percentage of damage to each type of structure (Table ndash B)
Grade of damage to different types of structures (Table ndash C)
Details of Intensity Scale (Table ndash D)
The main features of MSK intensity scale are as follows
Table ndash A Types of Structures (Buildings)
Type of
Structures
Definitions
A Building in field-stone rural structures unburnt ndash brick houses clay houses
B Ordinary brick buildings buildings of large block and prefabricated type half
timbered structures buildings in natural hewn stone
C Reinforced buildings well built wooden structures
Table ndash B Definition of Quantity
Quantity Percentage
Single few About 5 percent
Many About 50 percent
Most About 75 percent
Table ndash C Classification of Damage to Buildings
Grade Definitions Descriptions
G1 Slight damage Fine cracks in plaster fall of small pieces of plaster
G2 Moderate damage Small cracks in plaster fall of fairly large pieces of plaster
pantiles slip off cracks in chimneys parts of chimney fall down
G3 Heavy damage Large and deep cracks in plaster fall of chimneys
G4 Destruction Gaps in walls parts of buildings may collapse separate parts of
the buildings lose their cohesion and inner walls collapse
G5 Total damage Total collapse of the buildings
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Table ndash D Details of Intensity Scale
Intensity Descriptions
I Not noticeable The intensity of the vibration is below the limits of sensibility
the tremor is detected and recorded by seismograph only
II Scarcely noticeable
(very slight)
Vibration is felt only by individual people at rest in houses
especially on upper floors of buildings
III Weak partially
observed only
The earthquake is felt indoors by a few people outdoors only in
favourable circumstances The vibration is like that due to the
passing of a light truck Attentive observers notice a slight
swinging of hanging objects somewhat more heavily on upper
floors
IV Largely observed The earthquake is felt indoors by many people outdoors by few
Here and there people awake but no one is frightened The
vibration is like that due to the passing of a heavily loaded truck
Windows doors and dishes rattle Floors and walls crack
Furniture begins to shake Hanging objects swing slightly Liquid
in open vessels are slightly disturbed In standing motor cars the
shock is noticeable
V Awakening
a) The earthquake is felt indoors by all outdoors by many Many
people awake A few run outdoors Animals become uneasy
Buildings tremble throughout Hanging objects swing
considerably Pictures knock against walls or swing out of
place Occasionally pendulum clocks stop Unstable objects
overturn or shift Open doors and windows are thrust open
and slam back again Liquids spill in small amounts from
well-filled open containers The sensation of vibration is like
that due to heavy objects falling inside the buildings
b) Slight damages in buildings of Type A are possible
c) Sometimes changes in flow of springs
VI Frightening
a) Felt by most indoors and outdoors Many people in buildings
are frightened and run outdoors A few persons loose their
balance Domestic animals run out of their stalls In few
instances dishes and glassware may break and books fall
down Heavy furniture may possibly move and small steeple
bells may ring
b) Damage of Grade 1 is sustained in single buildings of Type B
and in many of Type A Damage in few buildings of Type A
is of Grade 2
c) In few cases cracks up to widths of 1cm possible in wet
ground in mountains occasional landslips change in flow of
springs and in level of well water are observed
VII Damage of buildings
a) Most people are frightened and run outdoors Many find it
difficult to stand The vibration is noticed by persons driving
motor cars Large bells ring
b) In many buildings of Type C damage of Grade 1 is caused in
many buildings of Type B damage is of Grade 2 Most
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buildings of Type A suffer damage of Grade 3 few of Grade
4 In single instances landslides of roadway on steep slopes
crack inroads seams of pipelines damaged cracks in stone
walls
c) Waves are formed on water and is made turbid by mud stirred
up Water levels in wells change and the flow of springs
changes Sometimes dry springs have their flow resorted and
existing springs stop flowing In isolated instances parts of
sand and gravelly banks slip off
VIII Destruction of
buildings
a) Fright and panic also persons driving motor cars are
disturbed Here and there branches of trees break off Even
heavy furniture moves and partly overturns Hanging lamps
are damaged in part
b) Most buildings of Type C suffer damage of Grade 2 and few
of Grade 3 Most buildings of Type B suffer damage of Grade
3 Most buildings of Type A suffer damage of Grade 4
Occasional breaking of pipe seams Memorials and
monuments move and twist Tombstones overturn Stone
walls collapse
c) Small landslips in hollows and on banked roads on steep
slopes cracks in ground up to widths of several centimetres
Water in lakes becomes turbid New reservoirs come into
existence Dry wells refill and existing wells become dry In
many cases change in flow and level of water is observed
IX General damage of
buildings
a) General panic considerable damage to furniture Animals run
to and fro in confusion and cry
b) Many buildings of Type C suffer damage of Grade 3 and a
few of Grade 4 Many buildings of Type B show a damage of
Grade 4 and a few of Grade 5 Many buildings of Type A
suffer damage of Grade 5 Monuments and columns fall
Considerable damage to reservoirs underground pipes partly
broken In individual cases railway lines are bent and
roadway damaged
c) On flat land overflow of water sand and mud is often
observed Ground cracks to widths of up to 10 cm on slopes
and river banks more than 10 cm Furthermore a large
number of slight cracks in ground falls of rock many
landslides and earth flows large waves in water Dry wells
renew their flow and existing wells dry up
X General destruction of
building
a) Many buildings of Type C suffer damage of Grade 4 and a
few of Grade 5 Many buildings of Type B show damage of
Grade 5 Most of Type A have destruction of Grade 5
Critical damage to dykes and dams Severe damage to
bridges Railway lines are bent slightly Underground pipes
are bent or broken Road paving and asphalt show waves
b) In ground cracks up to widths of several centimetres
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sometimes up to 1m Parallel to water courses occur broad
fissures Loose ground slides from steep slopes From river
banks and steep coasts considerable landslides are possible
In coastal areas displacement of sand and mud change of
water level in wells water from canals lakes rivers etc
thrown on land New lakes occur
XI Destruction
a) Severe damage even to well built buildings bridges water
dams and railway lines Highways become useless
Underground pipes destroyed
b) Ground considerably distorted by broad cracks and fissures
as well as movement in horizontal and vertical directions
Numerous landslips and falls of rocks The intensity of the
earthquake requires to be investigated specifically
XII Landscape changes
a) Practically all structures above and below ground are greatly
damaged or destroyed
b) The surface of the ground is radically changed Considerable
ground cracks with extensive vertical and horizontal
movements are observed Falling of rock and slumping of
river banks over wide areas lakes are dammed waterfalls
appear and rivers are deflected The intensity of the
earthquake requires to be investigated specially
442 तवतभनन सकलो ो की िीवरिा मलो ो की िलना Comparison of Intensity Values of
Different Scales
443 तवतभनन पररमाण और िीवरिा क भको प का परभाव Effect of Earthquake of various
Magnitude and Intensity
The following describes the typical effects of earthquakes of various magnitudes near the
epicenter The values are typical only They should be taken with extreme caution since intensity
and thus ground effects depend not only on the magnitude but also on the distance to the
epicenter the depth of the earthquakes focus beneath the epicenter the location of the epicenter
and geological conditions (certain terrains can amplify seismic signals)
Fig 45 Comparison of Intensity Values of Different Scales
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Magnitude Description Mercalli
intensity
Average earthquake effects Average
frequency of
occurrence
(estimated)
10-19 Micro I Micro earthquakes not felt or felt rarely
Recorded by seismographs
Continualseveral
million per year
20-29 Minor I to II Felt slightly by some people No damage to
buildings
Over one million
per year
30-39 III to IV Often felt by people but very rarely causes
damage Shaking of indoor objects can be
noticeable
Over 100000 per
year
40-49 Light IV to VI Noticeable shaking of indoor objects and
rattling noises Felt by most people in the
affected area Slightly felt outside
Generally causes none to minimal damage
Moderate to significant damage very
unlikely Some objects may fall off shelves
or be knocked over
10000 to 15000
per year
50-59 Moderate VI to
VIII
Can cause damage of varying severity to
poorly constructed buildings At most none
to slight damage to all other buildings Felt
by everyone
1000 to 1500 per
year
60-69 Strong VII to X Damage to a moderate number of well-built
structures in populated areas Earthquake-
resistant structures survive with slight to
moderate damage Poorly designed
structures receive moderate to severe
damage Felt in wider areas up to hundreds
of mileskilometers from the epicenter
Strong to violent shaking in epicentral area
100 to 150 per
year
70-79 Major VIII or
Greater
Causes damage to most buildings some to
partially or completely collapse or receive
severe damage Well-designed structures
are likely to receive damage Felt across
great distances with major damage mostly
limited to 250 km from epicenter
10 to 20 per year
80-89 Great Major damage to buildings structures
likely to be destroyed Will cause moderate
to heavy damage to sturdy or earthquake-
resistant buildings Damaging in large
areas Felt in extremely large regions
One per year
90 and
greater
At or near total destruction ndash severe damage
or collapse to all buildings Heavy damage
and shaking extends to distant locations
Permanent changes in ground topography
One per 10 to 50
years
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45 भको प तनगरानी और सवाओो क तलए एजतसयो ो Agencies for Earthquake Monitoring and
Services
Centre for Seismology (CS) in Indian Meteorological Department (IMD) under Ministry of
Earth Sciences is nodal agency of Government of India dealing with various activities in
the field of seismology and allied disciplines and is responsible for monitoring seismic
activity in and around the country
The major activities currently being pursued by the Centre for Seismology (CS) include
a) Earthquake monitoring on 24X7 basis including real time seismic monitoring for early
warning of tsunamis
b) Operation and maintenance of national seismological network and local networks
c) Seismological data centre and information services
d) Seismic hazard and risk related studies
e) Field studies for aftershock swarm monitoring site response studies
f) Earthquake processes and modelling etc
These activities are being managed by various unitsgroups of the Centre for Seismology
(CS) as detailed below
1) Centre for Seismology (CS) is maintaining a country wide National Seismological
Network (NSN) consisting of a total of 82 seismological stations spread over the
entire length and breadth of the country This includes
a) 16-station V-SAT based digital seismic telemetry system around National Capital
Territory (NCT) of Delhi
b) 20-station VSAT based real time seismic monitoring network in North East region
of the country
(c) 17-station Real Time Seismic Monitoring Network (RTSMN) to monitor and
report large magnitude under-sea earthquakes capable of generating tsunamis on
the Indian coastal regions
2) The remaining stations are of standalone analog type
3) A Control Room is in operation on a 24X7 basis at premises of IMD Headquarters in
New Delhi with state-of-the art facilities for data collection processing and
dissemination of information to the concerned user agencies
4) India represented by CSIMD is a permanent Member of the International
Seismological Centre (ISC) UK
5) Seismological Bulletins of CSIMD are shared regularly with International
Seismological Centre (ISC) UK for incorporation in the ISCs Monthly Seismological
Bulletins which contain information on earthquakes occurring all across the globe
6) Towards early warning of tsunamis real-time continuous seismic waveform data of
three IMD stations viz Portblair Minicoy and Shillong is shared with global
community through IRIS (Incorporated Research Institutions of Seismology)
Washington DC USA
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अधयाय Chapter ndash 5
भवन म भको प परतिरोध म सधार क तलए सामानय तसदाोि General Principle for improving Earthquake Resistance in Building
51 िलकापन Lightness
Since the earthquake force is a function of mass the building should be as light as possible
consistent with structural safety and functional requirements Roofs and upper storeys of
buildings in particular should be designed as light as possible
52 तनमायण की तनरोिरिा Continuity of Construction
As far as possible all parts of the building should be tied together in such a manner that
the building acts as one unit
For integral action of building roof and floor slabs should be continuous throughout as
far as possible
Additions and alterations to the structures should be accompanied by the provision of
positive measures to establish continuity between the existing and the new construction
53 परोजककटोग एवो ससिि पाटटयस Projecting and Suspended Parts
Projecting parts should be avoided as far as possible If the projecting parts cannot be
avoided they should be properly reinforced and firmly tied to the main structure
Ceiling plaster should preferably be avoided When it is unavoidable the plaster should
be as thin as possible
Suspended ceiling should be avoided as far as possible Where provided they should be
light and adequately framed and secured
54 भवन की आकति Shape of Building
In order to minimize torsion and stress concentration the building should have a simple
rectangular plan
It should be symmetrical both with respect to mass and rigidity so that the centre of mass
and rigidity of the building coincide with each other
It will be desirable to use separate blocks of rectangular shape particularly in seismic
zones V and IV
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55 सतवधा जनक तबकडोग लआउट Preferred Building Layouts
Buildings having plans with shapes like L T E and Y shall preferably be separated into
rectangular parts by providing separation sections at appropriate places Typical examples are
shown in Fig 51
56 तवतभनन तदशाओो म शककत Strength in Various Directions
The structure shall have adequate strength against earthquake effects along both the horizontal
axes considering the reversible nature of earthquake forces
57 नी ोव Foundations
For the design of foundations the provisions of IS 1904 1986 in conjunctions with IS
1893 1984 shall generally be followed
The sub-grade below the entire area of the building shall preferably be of the same type of
the soil Wherever this is not possible a suitably located separation or crumple section shall
be provided
Loose fine sand soft silt and expansive clays should be avoided If unavoidable the
building shall rest either on a rigid raft foundation or on piles taken to a firm stratum
However for light constructions the following measures may be taken to improve the soil
on which the foundation of the building may rest
a) Sand piling and b) Soil stabilization
Structure shall not be founded on loose soil which will subside or liquefy during an
earthquake resulting in large differential settlement
58 छि एवो मोतजल Roofs and Floors
581 सपाट छि या फशय Flat roof or floor
Flat roof or floor shall not preferably be made of terrace of ordinary bricks supported on steel
timber or reinforced concrete joists nor they shall be of a type which in the event of an
earthquake is likely to be loosened and parts of all of which may fall If this type of construction
cannot be avoided the joists should be blocked at ends and bridged at intervals such that their
spacing is not altered during an earthquake
Fig 51 Typical Shapes of Building with Separation Sections [IS 4326 1993]
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582 ढलान वाली छि Pitched Roofs
For pitched roofs corrugated iron or asbestos sheets should be used in preference to
country Allahabad or Mangalore tiles or other loose roofing units
All roofing materials shall be properly tied to the supporting members
Heavy roofing materials should generally be avoided
583 सोवि छि Pent Roofs
All roof trusses should be supported on and fixed to timber band reinforced concrete band or
reinforced brick band The holding down bolts should have adequate length as required for
earthquake and wind forces
Where a trussed roof adjoins a masonry gable the ends of the purlins should be carried on and
secured to a plate or bearer which should be adequately bolted to timber reinforced concrete or
reinforced brick band at the top of gable end masonry
- At tie level all the trusses and the gable end should be provided with diagonal braces in plan
so as to transmit the lateral shear due to earthquake force to the gable walls acting as shear
walls at the ends
NOTE ndash Hipped roof in general have shown better structural behaviour during earthquakes than gable
ended roofs
584 जक मिराब Jack Arches
Jack arched roofs or floors where used should be provided with mild steel ties in all spans along
with diagonal braces in plan to ensure diaphragm actions
59 सीतढ़याो Staircases
The interconnection of the stairs with the adjacent floors should be appropriately treated by
providing sliding joints at the stairs to eliminate their bracing effect on the floors
Ladders may be made fixed at one end and freely resting at the other
Large stair halls shall preferably be separated from rest of the building by means of
separation or crumple section
Three types of stair construction may be adopted as described below
591 अलग सीतढ़याो Separated Staircases
One end of the staircase rests on a wall and the other end is carried by columns and beams which
have no connection with the floors The opening at the vertical joints between the floor and the
staircase may be covered either with a tread plate attached to one side of the joint and sliding on
the other side or covered with some appropriate material which could crumple or fracture during
an earthquake without causing structural damage
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The supporting members columns or walls are
isolated from the surrounding floors by means of
separation or crumple sections A typical
example is shown in Fig 52
592 तबलट-इन सीतढ़याो Built-in Staircase
When stairs are built monolithically with floors they can be protected against damage by
providing rigid walls at the stair opening An arrangement in which the staircase is enclosed by
two walls is given in Fig 53 (a) In such cases the joints as mentioned in respect of separated
staircases will not be necessary
The two walls mentioned above enclosing the staircase shall extend through the entire height of
the stairs and to the building foundations
Fig 53 (a) Rigidly Built-In Staircase [IS 4326 1993]
Fig 52 Separated Staircase
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593 सलाइतिोग जोड़ो ो वाली सीतढ़याो Staircases with Sliding Joints
In case it is not possible to provide rigid walls around stair openings for built-in staircase or to
adopt the separated staircases the staircases shall have sliding joints so that they will not act as
diagonal bracing (Fig 53 (b))
510 बॉकस परकार तनमायण Box Type Construction
This type of construction consists of prefabricated or in-situ masonry wall along with both the
axes of the building The walls support vertical loads and also act as shear walls for horizontal
loads acting in any direction All traditional masonry construction falls under this category In
prefabricated wall construction attention should be paid to the connections between wall panels
so that transfer of shear between them is ensured
511 अति सरकषा Fire Safety
Fire frequently follows an earthquake and therefore buildings should be constructed to make
them fire resistant in accordance with the provisions of relevant Indian Standards for fire safety
The relevant Indian Standards are IS 1641 1988 IS 1642 1989 IS 1643 1988 IS 1644 1988
and IS 1646 1986
Fig 53 (b) Staircase with Sliding Joint
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अधयाय Chapter ndash 6
भको प क दौरान आर सी भवनो ो क परदशयन पर सटरकचरल अतनयतमििाओो का परभाव Effect of Structural Irregularities on Performance of RC Buildings during Earthquakes
61 सटरकचरल अतनयतमििाओो का परभाव Effect of Structural Irregularities
There are numerous examples of past earthquakes in which the cause of failure of reinforced
concrete building has been ascribed to irregularities in configurations
Irregularities are mainly categorized as
(i) Horizontal Irregularities
(ii) Vertical Irregularities
62 कषतिज अतनयतमििाएो Horizontal Irregularities
Horizontal irregularities refer to asymmetrical plan shapes (eg L- T- U- F-) or discontinuities
in the horizontal resisting elements (diaphragms) such as cut-outs large openings re-entrant
corners and other abrupt changes resulting in torsion diaphragm deformations stress
concentration
Table ndash 61 Definitions of Irregular Buildings ndash Plan Irregularities (Fig 61)
S
No
Irregularity Type and Description
(i) Torsion Irregularity To be considered when floor diaphragms are rigid in their own
plan in relation to the vertical structural elements that resist the lateral forces Torsional
irregularity to be considered to exist when the maximum storey drift computed with
design eccentricity at one end of the structures transverse to an axis is more than 12
times the average of the storey drifts at the two ends of the structure
Fig 61 (a)
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(ii) Re-entrant Corners Plan configurations of a structure and its lateral force resisting
system contain re-entrant corners where both projections of the structure beyond the re-
entrant corner are greater than 15 percent of its plan dimension in the given direction
Fig 61 (b)
(iii) Diaphragm Discontinuity Diaphragms with abrupt discontinuities or variations in
stiffness including those having cut-out or open areas greater than 50 percent of the
gross enclosed diaphragm area or changes in effective diaphragm stiffness of more than
50 percent from one storey to the next
Fig 61 (c)
(iv) Out-of-Plane Offsets Discontinuities in a lateral force resistance path such as out-of-
plane offsets of vertical elements
Fig 61 (d)
(v) Non-parallel Systems The vertical elements
resisting the lateral force are not parallel to or
symmetric about the major orthogonal axes or the
lateral force resisting elements
Fig 61 (e)
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63 ऊरधायधर अतनयतमििाएो Vertical Irregularities
Vertical irregularities referring to sudden change of strength stiffness geometry and mass result
in irregular distribution of forces and or deformation over the height of building
Table ndash 62 Definition of Irregular Buildings ndash Vertical Irregularities (Fig 62)
S
No
Irregularity Type and Description
(i) a) Stiffness Irregularity ndash Soft Storey A soft storey is one in which the lateral stiffness is
less than 70 percent of that in the storey above or less than 80 percent of the average lateral
stiffness of the three storeys above
b) Stiffness Irregularity ndash Extreme Soft Storey A extreme soft storey is one in which the
lateral stiffness is less than 60 percent of that in the storey above or less than 70 percent of
the average stiffness of the three storeys above For example buildings on STILTS will fall
under this category
Fig 62 (a)
(ii) Mass Irregularity Mass irregularity shall be considered to exist where the seismic weight
of any storey is more than 200percent of that of its adjacent storeys The irregularity need
not be considered in case of roofs
Fig 62 (b)
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(iii) Vertical Geometric Irregularity Vertical geometric irregularity shall be considered to
exist where the horizontal dimension of the lateral force resisting system in any storey is
more than150 percent of that in its adjacent storey
Fig 62 (c)
(iv) In-Plane Discontinuity in Vertical Elements Resisting Lateral Force A in-plane offset of
the lateral force resisting elements greater than the length of those elements
Fig 62 (d)
(v) Discontinuity in Capacity ndash Weak Storey A weak storey is one in which the storey lateral
strength is less than 80 percent of that in the storey above The storey lateral strength is the
total strength of all seismic force resisting elements sharing the storey shear in the
considered direction
64 भवन तवनयास अतनयतमििाएो ndash सरसकयमए ववशलषण एव तनदमन क उपमय Building
Irregularities ndash Problems Analysis and Remedial Measures
The influence of irregularity on performance of building during earthquakes is presented to
account for the effects of these irregularities in analysis of problems and their solutions along
with the design
Vertical Geometric Irregularity when L2gt15 L1
In-Plane Discontinuity in Vertical Elements Resisting Weak Storey when Filt08Fi+ 1
Lateral Force when b gta
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Architectural problems Structural problems Remedial measures
Extreme heightdepth ratio
High overturning forces large drift causing non-structural damage foundation stability
Revive properties or special structural system
Extreme plan area Built-up large diaphragm forces Subdivide building by seismic joints
Extreme length depth ratio
Built-up of large lateral forces in perimeter large differences in resistance of two axes Experience greater variations in ground movement and soil conditions
Subdivide building by seismic joints
Variation in perimeter strength-stiffness
Torsion caused by extreme variation in strength and stiffness
Add frames and disconnect walls or use frames and lightweight walls
False symmetry Torsion caused by stiff asymmetric core Disconnect core or use frame with non-structural core walls
Re-entrant corners Torsion stress concentrations at the notches
Separate walls uniform box centre box architectural relief diagonal reinforcement
Mass eccentricities Torsion stress concentrations Reprogram or add resistance around mass to balance resistance and mass
Vertical setbacks and reverse setbacks
Stress concentration at notch different periods for different parts of building high diaphragm forces to transfer at setback
Special structural systems careful dynamic analysis
Soft storey frame Causes abrupt changes of stiffness at point of discontinuity
Add bracing add columns braced
Variation in column stiffness
Causes abrupt changes of stiffness much higher forces in stiffer columns
Redesign structural system to balance stiffness
Discontinuous shear wall Results in discontinuities in load path and stress concentration for most heavily loaded elements
Primary concern over the strength of lower level columns and connecting beams that support the load of discontinuous frame
Weak column ndash strong beam
Column failure occurs before beam short column must try and accommodate storey height displacement
Add full walls to reduce column forces or detach spandrels from columns or use light weight curtain wall with frame
Modification of primary structure
Most serious when masonry in-fill modifies structural concept creation of short stiff columns result in stress concentration
Detach in-fill or use light-weight materials
Building separation (Pounding)
Possibility of pounding dependent on building period height drift distance
Ensure adequate separation assuming opposite building vibrations
Coupled Incompatible deformation between walls and links
Design adequate link
Random Openings Seriously degrade capacity at point of maximum force transfer
Careful designing adequate space for reinforcing design
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अधयाय Chapter ndash 7
भवन की िायनातमक तवशषिाएा Dynamic Characteristics of Building
71 िायनातमक तवशषिाएा Dynamic Characteristics
Buildings oscillate during earthquake shaking The oscillation causes inertia force to be induced
in the building The intensity and duration of oscillation and the amount of inertia force induced
in a building depend on features of buildings called dynamic characteristics of building
The important dynamic characteristics of buildings are
a) Modes of Oscillation
b) Damping
A mode of oscillation of a building is defined by associated Natural Period and Deformed Shape
in which it oscillates Every building has a number of natural frequencies at which it offers
minimum resistance to shaking induced by external effects (like earthquakes and wind) and
internal effects(like motors fixed on it) Each of these natural frequencies and the associated
deformation shape of a building constitute a Natural Mode of Oscillation
The mode of oscillation with the smallest natural frequency (and largest natural period) is called
the Fundamental Mode the associated natural period T1is called the Fundamental Natural
Period
72 पराकतिक अवतध Natural Period
Natural Period (Tn) of a building is the time taken by it to undergo one complete cycle of
oscillation It is an inherent property of a building controlled by its mass m and stiffness k These
three quantities are related by
Its unit is second (s)
73 पराकतिक आवततत Natural Frequency
The reciprocal (1Tn) of natural period of a building is called the Natural Frequency fn its unit is
Hertz (Hz)
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74 पराकतिक अवतध को परभातवि करन वाल कारक Factors influencing Natural Period
741 कठोरिा का परभाव Effect of Stiffness Stiffer buildings have smaller natural period
742 दरवयमान का परभाव Effect of Mass Heavier buildings have larger natural period
743 कॉलम अतभतवनयास का परभाव Effect of Column Orientation Buildings with larger
column dimension oriented in the direction reduces the translational natural period of oscillation
in that direction
Fig 72 Effect of Mass
Fig 71 Effect of Stiffness
Fig 73 Effect of Column Orientation
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744 भवन की ऊो चाई का परभाव Effect of Building Height Taller buildings have larger
natural period
745 Unreinforced तचनाई भराव का परभाव Effect of Unreinforced Masonry Infills Natural
Period of building is lower when the stiffness contribution of URM infill is considered
Fig 75 Effect of Building Height
Fig 74 Effect of Building Height
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75 Mode आकति Mode Shape
Mode shape of oscillation associated with a natural period of a building is the deformed shape of
the building when shaken at the natural period Hence a building has as many mode shapes as
the number of natural periods
The deformed shape of the building associated with oscillation at fundamental natural period is
termed its first mode shape Similarly the deformed shapes associated with oscillations at
second third and other higher natural periods are called second mode shape third mode shape
and so on respectively
Fundamental Mode Shape of Oscillation
As shown in Fig 76 there are three basic modes of oscillation namely
1 Pure translational along X-direction
2 Pure translational along Y-direction and
3 Pure rotation about Z-axis
Regular buildings
These buildings have pure mode shapesThe Basic modes of oscillation ie two translational and
one rotational mode shapes
Irregular buildings
These buildings that have irregular geometry non-uniform distribution of mass and stiffness in
plan and along the height have mode shapes which are a mixture of these pure mode shapes
Each of these mode shapes is independent implying it cannot be obtained by combining any or
all of the other mode shapes
a) Fundamental and two higher translational modes of oscillation along X-direction of a
five storey benchmark building First modes shape has one zero crossing of the un-deformed
position second two and third three
Fig 76 Basic modes of oscillation
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b) Diagonal modes of oscillation First three modes of oscillation of a building symmetric in
both directions in plan first and second are diagonal translational modes and third rotational
c) Effect of modes of oscillation on column bending Columns are severely damaged while
bending about their diagonal direction
Fig 77 Fundamental and two higher translational modes of oscillation
along X-direction of a five storey benchmark building
Fig 78 Diagonal modes of oscillation
Fig 79 Effect of modes of oscillation on column bending
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76 Mode आकतियो ो को परभातवि करन वाल कारक Factors influencing Mode Shapes
761 Effect of relative flexural stiffness of structural elements Fundamental translational
mode shape changes from flexural-type to shear-type with increase in beam flexural stiffness
relative to that of column
762 Effect of axial stiffness of vertical members Fundamental translational mode shape
changes from flexure-type to shear-type with increase in axial stiffness of vertical members
Fig 710 Effect of relative flexural stiffness of structural elements
Fig 711 Effect of axial stiffness of vertical members
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763 Effect of degree of fixity at member ends Lack of fixity at beam ends induces flexural-
type behaviour while the same at column bases induces shear-type behaviour to the fundamental
translational mode of oscillation
Fig 712 Effect of degree of fixity at member ends
764 Effect of building height Fundamental translational mode shape of oscillation does not
change significantly with increase in building height unlike the fundamental translational natural
period which does change
Fig 713 Effect of building height
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765 Influence of URM Infill Walls in Mode Shape of RC frame Buildings Mode shape of
a building obtained considering stiffness contribution of URM is significantly different from that
obtained without considering the same
77 सोरचना की परतितकरया Response of Structure
The earthquakes cause vibratory motion which is cyclic about the equilibrium The structural
response is vibratory (Dynamic) and it is cyclic about the equilibrium position of structure The
fundamental natural frequency of most civil engineering structures lie in the range of 01 sec to
30 sec or so This is also the range of frequency content of earthquake-generated ground
motions Hence the ground motion imparts considerable amount of energy to the structures
Initially the structure responds elastically to the ground motion however as its yield capacity is
exceeded the structure responds in an inelastic manner During the inelastic response stiffness
and energy dissipation properties of the structure are modified
Response of the structure to a given strong ground motion depends not only on the properties of
input ground motion but also on the structural properties
78 तिजाइन सकटर म Design Spectrum
The design spectrum is a design specification which is arrived at by considering all aspects The
design spectrum may be in terms of acceleration velocity or displacement
Fig 714 Influence of URM Infill Walls in Mode Shape of RC frame Buildings
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Since design spectrum is a specification for design it cannot be viewed in isolation without
considering the other factors that go into the design process One must concurrently specify
a) The procedure to calculate natural period of the structure
b) The damping to be used for a given type of structure
c) The permissible stresses and strains load factors etc
Unless this information is part of a design spectrum the design specification is incomplete
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अधयाय Chapter ndash 8
डिजमइन पमशवा बलो क तनधमारण क ललए कोि आधमररि िरीकम Code based Procedure for Determination of Design Lateral Loads
81 भको पी तिजाइन की तफलोसफ़ी Philosophy of Seismic Design
Design of earthquake effect is not termed as Earthquake Proof Design Actual forces that appear
on structure during earthquake are much greater than the design forces Complete protection
against earthquake of all size is not economically feasible and design based alone on strength
criteria is not justified Earthquake demand is estimated only based on concept of probability of
exceedance Design of earthquake effect is therefore termed as Earthquake Resistant Design
against the probable value of demand
Maximum Considered Earthquake (MCE) The earthquake corresponding to the Ultimate
Safety Requirement is often called as Maximum Considered Earthquake
Design Basis Earthquake (DBE) It is defined as the Maximum Earthquake that reasonably can
be expected to experience at the site during lifetime of structure
The philosophy of seismic design is to ensure that structures possess at least a minimum strength
to
(i) resist minor (lt DBE) which may occur frequently without damage
(ii) resist moderate earthquake (DBE) without significant structural damage through some
non-structural damage
(iii) resist major earthquake (MCE) without collapse
82 भको पी तवशलषण क तलए िरीक Methods for Seismic Analysis
The response of a structure to ground vibrations is a function of the nature of foundation soil
materials form size and mode of construction of structures and duration and characteristics of
ground motion Code specifies design forces for structures standing on rock or firm soils which
do not liquefy or slide due to loss of strength during ground motion
Analysis is carried out by
a- Dynamic analysis procedure [Clause 78 of IS 1893 (Part I) 2002]
b- Simplified method referred as Lateral Force Procedure [Clause 75 of IS 1893 (Part I)
2002] also recognized as Equivalent Lateral Force Procedure or Equivalent Static
Procedure in the literature
The main difference between the equivalent lateral force procedure and dynamic analysis
procedure lies in the magnitude and distribution of lateral forces over the height of the buildings
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In the dynamic analysis procedure the lateral forces are based on the properties of the natural
vibration modes of the building which are determined by the distribution of mass and stiffness
over height In the equivalent lateral force procedures the magnitude of forces is based on an
estimation of the fundamental period and on the distribution of forces as given by simple
formulae appropriate for regular buildings
83 िायनातमक तवशलषण Dynamic Analysis
Dynamic analysis shall be performed to obtain the design seismic force and its distribution to
different levels along the height of the building and to the various lateral load resisting elements
for the following buildings
a) Regular buildings ndash Those greater than 40 m in height in Zones IV and V and those greater
than 90 m in height in Zones II and III Modelling as per Para 7845 of IS 1893 (Part 1)
2002 can be used
b) Irregular buildings (as defined in Table ndash 61 and Table ndash 62 of Chapter - 6) ndash All framed
buildings higher than 12m in Zones IV and V and those greater than 40m in height in Zones
II and III
84 पारशय बल परतकरया Lateral Force Procedure
The random earthquake ground motions which cause the structure to vibrate can be resolved in
any three mutually perpendicular directions The predominant direction of ground vibration is
usually horizontal
The codes represent the earthquake-induced inertia forces in the form of design equivalent static
lateral force This force is called as the Design Seismic Base Shear VB VB remains the primary
quantity involved in force-based earthquake-resistant design of buildings
The Design Seismic Base Shear VB is given by
Where Ah = Design horizontal seismic coefficient for a structure
=
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Z = Zone Factor
It is for the Maximum Considered Earthquake (MCE) and service life of structure in a zone
Generally Design Basis Earthquake (DBE) is half of Maximum Considered Earthquake
(MCE) The factor 2 in the denominator of Z is used so as to reduce the MCE zone factor to
the factor for DBE
The value of Ah will not be taken less than Z2 whatsoever the value of IR
The value of Zone Factor is given in Table ndash 81
Table ndash 81 Zone Factor Z[IS 1893 (Part 1) 2002]
Seismic Zone II III IV V
Seismic Intensity Low Moderate Severe Very Severe
Zone Factor Z 010 016 024 036
I = Importance Factor
Value of importance factor depends upon the functional use of the structures characterized
by hazardous consequences of its failure post-earthquake functional needs historical value
or economic importance (as given in Table ndash 82)
Table ndash 82 Importance Factors I [IS 1893 (Part 1) 2002]
S
No
Structure Importance
Factor
(i) Important service and community buildings such as hospitals schools
monumental structures emergency buildings like telephone exchange
television stations radio stations railway stations fire station buildings
large community halls like cinemas assembly halls and subway stations
power stations
15
(ii) AU other buildings 10
Note
1 The design engineer may choose values of importance factor I greater than those
mentioned above
2 Buildings not covered in S No (i) and (ii) above may be designed for higher value of I
depending on economy strategy considerations like multi-storey buildings having
several residential units
3 This does not apply to temporary structures like excavations scaffolding etc of short
duration
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R = Response Reduction Factor
To make normal buildings economical design code allows some damage for reducing the
cost of construction This philosophy is introduced with the help of Response reduction
factor R
The ratio (IR) shall not be greater than 10
Depending on the perceived seismic damage performance of the structure by ductile or brittle
deformations the values of R1)
for buildings are given in Table ndash 83 below
Table ndash 83 Response Reduction Factor1)
R for Building Systems [IS 1893 (Part 1) 2002]
S No Lateral Load Resisting System R Building Frame Systems (i) Ordinary RC moment-resisting frame ( OMRF )
2) 30
(ii) Special RC moment-resisting frame ( SMRF )3)
50 (iii) Steel frame with
a) Concentric braces 40 b) Eccentric braces 50
(iv) Steel moment resisting frame designed as per SP 6 (6) 50 Building with Shear Walls
4)
(v) Load bearing masonry wall buildings5)
a) Unreinforced 15 b) Reinforced with horizontal RC bands 25 c) Reinforced with horizontal RC bands and vertical bars at cornersof
rooms and jambs of openings 30
(vi) Ordinary reinforced concrete shear walls6)
30 (vii) Ductile shear walls
7) 40
Buildings with Dual Systems8)
(viii) Ordinary shear wall with OMRF 30 (ix) Ordinary shear wall with SMRF 40 (x) Ductile shear wall with OMRF 45 (xi) Ductile shear wall with SMRF 50 1) The values of response reduction factor are to be used for buildings with lateral load resisting
elements and not just for the lateral load resisting elements built in isolation 2) OMRF (Ordinary Moment-Resisting Frame) are those designed and detailed as per IS 456 or
IS 800 but not meeting ductile detailing requirement as per IS 13920 or SP 6 (6) respectively 3) SMRF (Special Moment-Resisting Frame) defined in 4152
As per 4152 SMRF is a moment-resisting frame specially detailed to provide ductile behaviour and comply with the requirements given in IS 4326 or IS 13920 or SP 6 (6)
4) Buildings with shear walls also include buildings having shear walls and frames but where a) frames are not designed to carry lateral loads or b) frames are designed to carry lateral loads but do not fulfil the requirements of lsquodual
systemsrsquo 5) Reinforcement should be as per IS 4326 6) Prohibited in zones IV and V 7) Ductile shear walls are those designed and detailed as per IS 13920 8) Buildings with dual systems consist of shear walls ( or braced frames ) and moment resisting
frames such that a) the two systems are designed to resist the total design force in proportion to their lateral
stiffness considering the interaction of the dual system at all floor levels and b) the moment resisting frames are designed to independently resist at least 25 percent of the
design seismic base shear
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Sag = Average Response Acceleration Coefficient
Net shaking of a building is a combined effect of the energy carried by the earthquake at
different frequencies and the natural period (T) of the building Code reflects this by
introducing a structural flexibility factor (Sag) also termed as Design Acceleration
Coefficient
Design Acceleration Coefficient (Sag) corresponding to 5 damping for different soil
types normalized to Peak Ground Acceleration (PAG) corresponding to natural period (T)
of structure considering soil structure interaction given by Fig 81 and associated expression
given below
Table ndash 84 gives multiplying factors for obtaining spectral values for various other damping
Table ndash 84 Multiplying Factors for Obtaining Values for Other Damping [IS 1893 (Part 1) 2002]
Damping () 0 2 5 7 10 15 20 25 30
Factors 320 140 100 090 080 070 060 055 050
85 को पन की मौतलक पराकतिक अवतध Fundamental Natural Period of Vibration
The approximate fundamental natural period of vibration (Ta)in seconds of a moment-resisting
frame building without brick infill panels may be estimated by the empirical expression
Ta = 0075 h075
for RC frame building
= 0085 h075
for steel frame building
Where h = Height of building in m This excludes the basement storeys where
basement walls are connected with the ground floor deck or fitted between
the building columns But it includes the basement storeys when they are
not so connected
Fig 81 Response Spectra for Rock and Soil Sitesfor5 Damping [IS 1893 (Part 1) 2002]
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The approximate fundamental natural period of vibration (Ta) in seconds of all other buildings
including moment-resisting frame buildings with brick infill panels may be estimated by the
empirical expression
Where h = Height of building in m as defined above
d = Base dimension of the building at the plinth level in m along the
considered direction of the lateral force
86 तिजाइन पारशय बल Design Lateral Force
The total design lateral force or design seismic base shear (VB) along any principal direction shall
be determined by the following expression
Where Ah= Design horizontal acceleration spectrum value as per 642 using the
fundamental natural period Ta as per 76 in the considered direction of
vibration and
W= Seismic weight of the building
The design lateral force shall first be computed for the building as a whole This design lateral
force shall then be distributed to the various floor levels
The overall design seismic force thus obtained at each floor level shall then be distributed to
individual lateral load resisting elements depending on the floor diaphragm action
87 तिजाइन बल का तविरण Distribution of Design Force
871 Vertical Distribution of Base Shear to Different Floor Levels
The Design Seismic Base Shear (VB) as computed above shall be distributed along the height of
the building as per the following expression
Where
Qi= Design lateral force at floor i
Wi = Seismic weight of floor i
hi = Height of floor i measured from base and
n= Number of storeys in the building is the number of levels at which the masses are
located
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872 Distribution of Horizontal Design Lateral Force to Different Lateral Force Resisting
Elements
1 In case of buildings whose floors are capable of providing rigid horizontal diaphragm
action the total shear in any horizontal plane shall be distributed to the various vertical
elements of lateral force resisting system assuming the floors to be infinitely rigid in the
horizontal plane
2 In case of building whose floor diaphragms cannot be treated as infinitely rigid in their
own plane the lateral shear at each floor shall be distributed to the vertical elements
resisting the lateral forces considering the in-plane flexibility of the diaphragms
Notes
1 A floor diaphragm shall be considered to be flexible if it deforms such that the maximum
lateral displacement measured from the chord of the deformed shape at any point of the
diaphragm is more than 15 times the average displacement of the entire diaphragm
2 Reinforced concrete monolithic slab-beam floors or those consisting of prefabricated
precast elements with topping reinforced screed can be taken rigid diaphragms
88 तिजाइन उदािरण Design Example ndash To determine Base Shear and its distribution
along Height of Building
Exercise ndash 1 Determine the total base shear as per IS 1893(Part 1)2002 and distribute the base
shear along the height of building to be used as school building in Bhuj Gujrat and founded on
Medium Soil Basic parameters for design of building are as follows
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ELEVATION
Solution
Basic Data
Following basic data is considered for analysis
i) Grade of Concrete M-25
ii) Grade of Steel Fe ndash 415 Tor Steel
iii) Density of Concrete 25 KNm3
iv) Density of Brick Wall 20 KNm3
v) Live Load for Roof 15 KNm2
vi) Live Load for Floor 50 KNm2
vii) Slab Thickness 150 mm
viii) Beam Size
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(a) 500 m Span 250 mm X 600 mm
(b) 400 m Span 250 mm X 550 mm
(c) 200 m Span 250 mm X 400 mm
ix) Column Size
(a) For 500 m Span 300 mm X 600 mm
(b) For 200 m Span 300 mm X 500 mm
Load Calculations
1 Dead Load Building is of G+4 Storeys
Approximate Covered Area of Building on GF = 30 X 8 = 240 m2
Approximate Covered Area of 1st 2
nd 3
rd amp 4
th Floor = 240 m
2
Total Floor Area = 5 X 240 = 1200 m2
Roof Area = 1 X 240 = 240 m2
(I) Slab
Self Wt of Slab = 015 X 25 = 375 KNm2
Wt of Floor Finish = 125 KNm2
------------------------------
Total = 500 KNm2
Dead Load of Slab per Floor = 240 X 5 = 1200 KN
Dead Load of Slab on Roof = 240 X 5 = 1200 KN
(II) Beam
Wt per m of 250 X 600 mm beam = 025 X 060 X 25 = 375 KNm
Wt per m of 250 X 550 mm beam = 025 X 055 X 25 = 344 KNm
Wt per m of 250 X 400 mm beam = 025 X 040 X 25 = 250 KNm
Weight of Beam per Floor
= (2 X 30 X 375) + (4 X 6 + 30) X 344 + (2 X 6 X 250)
= 225 + 18576 + 30 = 44076 KN [Say 44100 KN]
(III) Column
Wt per m of 300 X 600 mm column = 030 X 060 X 25 = 450 KNm
Wt per m of 300 X 500 mm column = 030 X 050 X 25 = 375 KNm
Weight of Column per Floor
= (12 X 3 X 450) + (6 X 3 X 375)
= 162 + 6750 = 22950 KN [Say 23000 KN]
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Walls
250 mm thick wall (including plaster) are provided Assuming 20 opening in the
wall ndash
Wt of Wall per m = 025 X 080 X 20 X 250
Wall Thickness Reduction Density Clear Height
= 1000 KNm
Wt of Parapet Wall per m = 0125 X 20 X 100 = 250 KNm
Wall Thickness Density Clear Height
Wt of Wall per Floor = 1000 X [30 X 3 + 2 X 2] = 940 KN
Wt of Wall at Roof = 250 X [30 X 2 + 8 X 2] = 190 KN
Total Dead Load ndash
(i) For Floor = Slab + Beam + Column + Wall
= 1200 + 441 + 230 + 940 = 2811 KN
(ii) For Roof = 1200 + 441 + 190 = 1831 KN
Slab Beam Parapet
2 Live Load Live Load on Floor = 40 KNm2
As per Table ndash 8 in Cl 731 of IS 1893 (Part 1)2002 ldquoage of Imposed Load to be
considered in Seismic Weight calculationrdquo
(i) Up to amp including 300 KNm2 = 25
(ii) Above 300 KNm2 = 50
Live Load on Floors to be = 200 KNm2 [ie 50 of 40 KNm
2]
considered for Earthquake Force
As per Cl 732 of IS 1893 (Part 1)2002 for calculating the design seismic force of the
structure the imposed load on roof need not be considered
Therefore Live Load on Roof = 000 KN
Seismic Weight due to Live Load
(i) For Floor = 240 X 2 = 480 KN
(ii) For Roof = 000 KN
3 Seismic Weight of Building
As per Cl 74 of IS 1893 (Part 1)2002
(i) For Floor = DL of Floor + LL on Floor
= 2811 + 480 = 3291 KN
(ii) For Roof = 1831 + 000 = 1831 KN
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Total Seismic Weight of Building = 5 X 3291 + 1 X 1831
W = 18286 KN
4 Determination of Base Shear
As per Cl 75 of IS 1893 (Part 1)2002 VB = Ah W
Where
VB = Base Shear
Ah = Design Horizontal Acceleration Spectrum
=
W = Seismic Wt of Building
Total height of Building above Ground Level = 1500 m
As per Cl 76 of IS 1893 (Part 1)2002 Fundamental Natural Period of Vibration for RC
Frame Building is
Ta = 0075 h075
= 0075 (15)075
= 0572 Sec
Average Response Acceleration Coefficient = 25
for 5 damping and Type II soil
Bhuj Gujrat is in Seismic Zone V
As per Table ndash 2 of IS 1893 (Part 1)2002
Zone Factor Z = 036
As per Table ndash 6 of IS 1893 (Part 1)2002
Impedance Factor I = 150
As per Table ndash 7 of IS 1893 (Part 1)2002
Response Reduction Factor for Ordinary R = 300
RC Moment-resisting Frame (OMRF) Building
Ah =
= (0362) X (1530) X (25)
= 0225
Base Shear VB = Ah W
= 0225 X 18286
= 411435 KN [Say 411400 KN]
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5 Vertical Distribution of Base Shear to Different Floors Levels
As per Cl 771 of IS 1893 (Part 1)2002
Where
Qi= Design lateral force at floor i
Wi = Seismic weight of floor i
hi = Height of floor i measured from base and
n= Number of storeys in the building is the number of levels at which the masses are
located
VB = 4114 KN
Storey
No
Mass
No
Wi hi Wi hi2
f =
Qi = VB x f
(KN)
Vi
(KN)
Roof 1 1831 18 593244 0268 1103 1103
4th
Floor 2 3291 15 740475 0333 1370 2473
3rd
Floor 3 3291 12 473904 0213 876 3349
2nd
Floor 4 3291 9 266571 0120 494 3843
1st Floor 5 3291 6 118476 0053 218 4061
Ground 6 3291 3 29619 0013 53 4114
= 2222289
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60
अधयाय Chapter ndash 9
ढााचागि सोरचना का तनमायण Construction of Framed Structure
91 गरतवाकषयण लोतिोग और भको प लोतिोग म आर सी तबकडोग का वयविार Behaviour of RC
Building in Gravity Loading and Earthquake Loading
In recent times reinforced concrete buildings have become common in India particularly in
towns and cities A typical RC building consists of horizontal members (beams and slabs) and
vertical members (columns and walls) The system is supported by foundations that rest on
ground The RC frame participates in resisting the gravity and earthquake forces as illustrated in
Fig 91
Gravity Loading
1 Load due to self weight and contents on buildings cause RC frames to bend resulting in
stretching and shortening at various locations
2 Tension is generated at surfaces that stretch
and compression at those that shorten
3 Under gravity loads tension in the beams is
at the bottom surface of the beam in the
central location and is at the top surface at
the ends
Earthquake Loading
1 It causes tension on beam and column faces
at locations different from those under
gravity loading the relative levels of this
tension (in technical terms bending
moment) generated in members are shown
in Figure
2 The level of bending moment due to
earthquake loading depends on severity of
shaking and can exceed that due to gravity
loading
3 Under strong earthquake shaking the beam
ends can develop tension on either of the
top and bottom faces
4 Since concrete cannot carry this tension
steel bars are required on both faces of
beams to resist reversals of bending
moment
5 Similarly steel bars are required on all faces of columns too
Fig 91 Earthquake shaking reverses tension and
compression in members ndash reinforcement is
required on both faces of members
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92 परबतलि को करीट इमारिो ो पर कषतिज भको प का परभाव Effect of Horizontal Earthquake Force
on RC Buildings
Earthquake shaking generates inertia forces in the building which are proportional to the
building mass Since most of the building mass is present at floor levels earthquake-induced
inertia forces primarily develop at the floor
levels These forces travel downwards -
through slab and beams to columns and walls
and then to the foundations from where they
are dispersed to the ground (Fig 92)
As inertia forces accumulate downwards from
the top of the building the columns and walls
at lower storeys experience higher earthquake-
induced forces and are therefore designed to be
stronger than those in storeys above
93 कषमिा तिजाइन सोकलपना Capacity Design Concept
(i) Let us take two bars of same length amp Cross-sectional area
1st bar ndash Made up of Brittle Material
2nd
bar ndash Made up of Ductile Material
(ii) Pull both the bars until they break
(iii) Plot the graph of bar force F versus bar
elongation Graph will be as given in Fig
93
(iv) It is observed that ndash
a) Brittle bar breaks suddenly on reaching its
maximum strength at a relatively small
elongation
b) Ductile bar elongates by a large amount
before it breaks
Materials used in building construction are steel
masonry and concrete Steel is ductile material
while masonry and concrete are brittle material
Capacity design concept ensures that the brittle
element will remain elastic at all loads prior to the
failure of ductile element Thus brittle mode of
failure ie sudden failure has been prevented
Fig 92 Total horizontal earthquake force in a
building increase downwards along its height
Fig 93 Tension Test on Materials ndash ductile
versus brittle materials
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The concept of capacity design is used to ensure post-yield ductile behaviour of a structure
having both ductile and brittle elements In this method the ductile elements are designed and
detailed for the design forces Then an upper-bound strength of the ductile elements is obtained
It is then expected that if the seismic force keeps increasing a point will come when these ductile
elements will reach their upper-bound strength and become plastic Clearly it is necessary to
ensure that even at that level of seismic force the brittle elements remain safe
94 लचीलापन और ऊजाय का अपवयय Ductility and Energy Dissipation
From strength point of view overdesigned structures need not necessarily demonstrate good
ductility By ductility of Moment Resisting Frames (MRF) one refers to the capacity of the
structure and its elements to undergo large deformations without loosing either strength or
stiffness It is important for a building in a seismic zone to be resilient ie absorb the shock from
the ground and dissipate this energy uniformly throughout the structure
In MRFs the dissipation of the input seismic energy takes place in the form of flexural yielding
and resulting in the formation of plastic moment hinges Due to cyclic nature of the flexural
effects both positive and negative plastic moment hinges may be formed
95 मजबि सतोभ ndash कमजोर बीम फलोसफ़ी lsquoStrong Column ndash Weak Beamrsquo Philosophy
Because beams are usually capable of developing large ductility than columns which are
subjected to significant compressive loads many building frames are designed based on the
lsquostrong column ndash weak beamrsquo philosophy Figure shows that for a frame designed according to
the lsquostrong column ndash weak beamrsquo philosophy to form a failure mechanism many more plastic
hinges have to be formed than a
frame designed according to the
ldquoweak column ndash strong beamrsquo
philosophy The frames designed
by the former approach dissipate
greater energy before failure
When this strategy is adopted in
design damage is likely to occur
first in beams When beams are
detailed properly to have large
ductility the building as a whole
can deform by large amounts
despite progressive damage caused
due to consequent yielding of
beams
Note If columns are made weaker they suffer severe local damage at the top and bottom of a
particular storey This localized damage can lead to collapse of a building although columns at
storeys above remain almost undamaged (Fig 94)
Fig 94 Two distinct designs of buildings that result in different
earthquake performancesndashcolumns should be stronger than beams
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For a building to remain safe during earthquake shaking columns (which receive forces from
beams) should be stronger than beams and foundations (which receive forces from columns)
should be stronger than columns
96 कठोर िायाफराम तकरया Rigid Diaphragm Action
When beams bend in the vertical direction during earthquakes these thin slabs bend along with them And when beams move with columns in the horizontal direction the slab usually forces the beams to move together with it In most buildings the geometric distortion of the slab is negligible in the horizontal plane this behaviour is known as the rigid diaphragm action This aspect must be considered during design (Fig 95)
97 सॉफट सटोरी तबकडोग क साथ ndash ओपन गराउोि सटोरी तबकडोग जो तक भको प क समय कमजोर िोिी ि
Building with Soft storey ndash Open Ground Storey Building that is vulnerable in
Earthquake
The buildings that have been constructed in recent times with a special feature - the ground storey is left open for the purpose of parking ie columns in the ground storey do not have any partition walls (of either masonry or RC) between them are called open ground storey buildings or buildings on stilts
An open ground storey building (Fig 96) having only columns in the ground storey and both partition walls and columns in the upper storeys have two distinct characteristics namely
(a) It is relatively flexible in the ground storey ie the relative horizontal displacement it undergoes in the ground storey is much larger than what each of the storeys above it does This flexible ground storey is also called soft storey
(b) It is relatively weak in ground storey ie
the total horizontal earthquake force it can carry in the ground storey is significantly smaller than what each of the storeys above it can carry Thus the open ground storey may also be a weak storey
Fig 95 Floor bends with the beam but moves all
columns at that level together
Fig 96 Upper storeys of open ground storey building
move together as a single block ndash such buildings are
like inverted pendulums
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The collapse of more than a hundred RC frame buildings with open ground storeys at
Ahmedabad (~225km away from epicenter) during the 2001 Bhuj earthquake has emphasized
that such buildings are extremely vulnerable under earthquake shaking
After the collapses of RC buildings in 2001 Bhuj earthquake the Indian Seismic Code IS 1893
(Part 1) 2002 has included special design provisions related to soft storey buildings
Firstly it specifies when a building should be considered as a soft and a weak storey building
Secondly it specifies higher design forces for the soft storey as compared to the rest of the
structure
The Code suggests that the forces in the columns
beams and shear walls (if any) under the action of
seismic loads specified in the code may be
obtained by considering the bare frame building
(without any infills) However beams and
columns in the open ground storey are required to
be designed for 25 times the forces obtained
from this bare frame analysis (Fig 97)
For all new RC frame buildings the best option is
to avoid such sudden and large decrease in stiffness
andor strength in any storey it would be ideal to
build walls (either masonry or RC walls) in the
ground storey also Designers can avoid dangerous
effects of flexible and weak ground storeys by
ensuring that too many walls are not discontinued
in the ground storey ie the drop in stiffness and
strength in the ground storey level is not abrupt due
to the absence of infill walls (Fig 98)
The existing open ground storey buildings need to be strengthened suitably so as to prevent them
from collapsing during strong earthquake shaking The owners should seek the services of
qualified structural engineers who are able to suggest appropriate solutions to increase seismic
safety of these buildings
971 भरी हई दीवार In-Fill Walls
When columns receive horizontal forces at floor
levels they try to move in the horizontal direction
but masonry walls tend to resist this movement
Due to their heavy weight and thickness these
walls attract rather large horizontal forces
However since masonry is a brittle material these
walls develop cracks once their ability to carry
horizontal load is exceeded Thus infill walls act
like sacrificial fuses in buildings they develop
Fig 99 Infill walls move together with the
columns under earthquake shaking
Fig 97 Open ground storey building ndashassumptions
made in current design practice are not consistent
with the actual structure
Fig 98 Avoiding open ground storey problem ndash
continuity of walls in ground storey is preferred
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cracks under severe ground shaking but help share the load of the beams and columns until
cracking Earthquake performance of infill walls is enhanced by mortars of good strength
making proper masonry courses and proper packing of gaps between RC frame and masonry
infill walls (Fig 99)
98 भको प क दौरान लघ कॉलम वाली इमारिो ो का वयविार Behavior of Buildings with Short
Columns during Earthquakes
During past earthquakes reinforced concrete (RC) frame buildings that have columns of different heights within one storey suffered more damage in the shorter columns as compared to taller columns in the same storey
Two examples of buildings with short columns are shown in Fig 910 ndash (a) buildings on a sloping ground and (b) buildings with a mezzanine floor
Poor behaviour of short columns is due to the fact that in an earthquake a tall column and a short column of same cross-section move horizontally by same amount
However the short column is stiffer as compared
to the tall column and it attracts larger earthquake
force Stiffness of a column means resistance to
deformation ndash the larger is the stiffness larger is
the force required to deform it If a short column is
not adequately designed for such a large force it
can suffer significant damage during an
earthquake This behaviour is called Short Column
Effect (Fig 911)
In new buildings short column effect should be
avoided to the extent possible during architectural
design stage itself When it is not possible to avoid
short columns this effect must be addressed in
structural design The IS13920-1993for ductile
detailing of RC structures requires special
confining reinforcement to be provided over the
full height of columns that are likely to sustain
short column effect
Fig 910 Buildings with short columns ndash two
explicit examples of common occurrences
Fig 911 Short columns are stiffer and attract larger
forces during earthquakes ndash this must be accounted
for in design
Fig 912 Details of reinforcement in a building with
short column effect in some columns ndashadditional
special requirements are given in IS13920- 1993 for
the short columns
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The special confining reinforcement (ie closely spaced closed ties) must extend beyond the
short column into the columns vertically above and below by a certain distance as shown in
Fig 912
In existing buildings with short columns different retrofit solutions can be employed to avoid
damage in future earthquakes Where walls of partial height are present the simplest solution is
to close the openings by building a wall of full height ndash this will eliminate the short column
effect If that is not possible short columns need to be strengthened using one of the well
established retrofit techniques The retrofit solution should be designed by a qualified structural
engineer with requisite background
99 भको प परतिरोधी इमारिो ो की लचीलापन आवशयकिाएा Ductility requirements of
Earthquake Resistant Buildings
The primary members of structure such as beams and columns are subjected to stress reversals
from earthquake loads The reinforcement provided shall cater to the needs of reversal of
moments in beams and columns and at their junctions
Earthquake motion often induces forces large enough to cause inelastic deformations in the
structure If the structure is brittle sudden failure could occur But if the structure is made to
behave ductile it will be able to sustain the earthquake effects better with some deflection larger
than the yield deflection by absorption of energy Therefore besides the design for strength of
the frame ductility is also required as an essential element for safety from sudden collapse during
severe shocks
The ductility requirements will be deemed to be satisfied if the conditions given as in the
following are achieved
1 For all buildings which are more than 3 storeys in height the minimum grade of concrete
shall be M20 ( fck = 20 MPa )
2 Steel reinforcements of grade Fe 415 (IS 1786 1985) or less only shall be used
However high strength deformed steel bars produced by the thermo-mechanical treatment
process of grades Fe 500 and Fe 550 having elongation more than 145 percent and conforming
to other requirements of IS 1786 1985 may also be used for the reinforcement
910 बीम तजनह आर सी इमारिो ो म भको प बलो ो का तवरोध करन क तलए िाला जािा ि Beams that
are required to resist Earthquake Forces in RC Buildings
In RC buildings the vertical and horizontal members (ie the columns and beams) are built
integrally with each other Thus under the action of loads they act together as a frame
transferring forces from one to another
Beams in RC buildings have two sets of steel reinforcement (Fig 913) namely
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(a) long straight bars (called longitudinal bars)
placed along its length and
(b) closed loops of small diameter steel bars (called
stirrups)placed vertically at regular intervals
along its full length
Beams sustain two basic types of failures namely
(i) Flexural (or Bending) Failure
As the beam sags under increased loading it can
fail in two possible ways (Fig 914)
If relatively more steel is present on the tension
face concrete crushes in compression this is
a brittle failure and is therefore undesirable
If relatively less steel is present on the
tension face the steel yields first (it keeps
elongating but does not snap as steel has
ability to stretch large amounts before it
snaps and redistribution occurs in the beam
until eventually the concrete crushes in
compression this is a ductile failure and
hence is desirable Thus more steel on
tension face is not necessarily desirable The
ductile failure is characterized with many
vertical cracks starting from the stretched
beam face and going towards its mid-depth
(ii) Shear Failure
A beam may also fail due to shearing action A shear crack is inclined at 45deg to the horizontal it
develops at mid-depth near the support and grows towards the top and bottom faces Closed loop
stirrups are provided to avoid such shearing action Shear damage occurs when the area of these
stirrups is insufficient Shear failure is brittle and therefore shear failure must be avoided in the
design of RC beams
Longitudinal bars are provided to resist flexural
cracking on the side of the beam that stretches
Since both top and bottom faces stretch during
strong earthquake shaking longitudinal steel bars
are required on both faces at the ends and on the
bottom face at mid-length (Fig 915)
Fig 914 Two types of damage in a beam flexure
damage is preferred Longitudinal bars resist the
tension forces due to bending while vertical stirrups
resist shear forces
Fig 913 Steel reinforcement in beams ndash stirrups
prevent longitudinal bars from bending outwards
Fig 915 Location and amount of longitudinal steel
bars in beams ndash these resist tension due to flexure
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Designing a beam involves the selection of its material properties (ie grades of steel bars
and concrete) and shape and size these are usually selected as a part of an overall design
strategy of the whole building
The amount and distribution of steel to be provided in the beam must be determined by
performing design calculations as per IS 456-2000 and IS 13920-1993
911 फलकसचरल ममबसय क तलए सामानय आवशयकिाएा General Requirements for Flexural
Members
These members shall satisfy the following requirements
The member shall preferably have a width-to-depth ratio of more than 03
The width of the member shall not be less than 200 mm
The depth D of the member shall preferably be not more than 14 of the clear span
The factored axial stress on the member under earthquake loading shall not exceed 01fck
9111 अनदधयय सदढीकरण Longitudinal Reinforcement
a) The top as well as bottom reinforcement shall consist of at least two bars throughout the
member length
b) The tension steel ratio on any face at any section shall not be less than ρmin = 024 where fck
and fy are in MPa
The positive steel at a joint face must be at least equal to half the negative steel at that face
The steel provided at each of the top and bottom face of the member at any section along its
length shall be at least equal to one-fourth of the maximum negative moment steel provided
at the face of either joint It may be clarified that
redistribution of moments permitted in IS 456
1978 (clause 361) will be used only for vertical
load moments and not for lateral load moments
In an external joint both the top and the bottom
bars of the beam shall be provided with anchorage
length beyond the inner face of the column equal
to the development length in tension plus 10 times
the bar diameter minus the allowance for 90 degree
bend(s) (as shown in Fig 916) In an internal joint
both face bars of the beam shall be taken
continuously through the column
Fig 916 Anchorage of Beam Bars in an External Joint (IS 13920 1993)
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9112 अनदधयय सदढीकरण की सपलाइतसोग Splicing of longitudinal reinforcement
The longitudinal bars shall be spliced only if hoops are
provided over the entire splice length at a spacing not
exceeding 150 mm (as shown in Fig 917) The lap length
shall not be less than the bar development length in tension
Lap splices shall not be provided (a) within a joint (b)
within a distance of 2d from joint face and (c) within a
quarter length of the member where flexural yielding may
generally occur under the effect of earthquake forces Not
more than 50 percent of the bars shall be spliced at one
section
Use of welded splices and mechanical connections may also be made as per 25252 of
IS 456-1978 However not more than half the reinforcement shall be spliced at a section
where flexural yielding may take place
9113 वब सदढीकरण Web Reinforcement
Web reinforcement shall consist of vertical hoops A vertical hoop is a closed stirrup having a
135deg hook with a 10 diameter extension (but
not lt 75 mm) at each end that is embedded
in the confined core [as shown in (a) of
Fig 918] In compelling circumstances it
may also be made up of two pieces of
reinforcement a U-stirrup with a 135deg hook
and a 10 diameter extension (but not lt 75
mm) at each end embedded in the confined
core and a crosstie [as shown in (b) of Fig
918] A crosstie is a bar having a 135deg hook
with a 10 diameter extension (but not lt 75
mm) at each end The hooks shall engage
peripheral longitudinal bars
912 कॉलम तजनह आर सी इमारिो ो म भको प बलो ो का तवरोध करन क तलए िाला जािा ि Columns that are required to resist Earthquake Forces in RC Buildings
Columns the vertical members in RC buildings contain two types of steel reinforcement
namely
(a) long straight bars (called longitudinal bars) placed vertically along the length and
(b) closed loops of smaller diameter steel bars (called transverse ties) placed horizontally at
regular intervals along its full length
Fig 917 Lap Splice in Beam
(IS 13920 1993)
Fig 918 Beam Web Reinforcement (IS 13920 1993)
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Columns can sustain two types of damage namely axial-flexural (or combined compression-
bending) failure and shear failure Shear damage is brittle and must be avoided in columns by
providing transverse ties at close spacing
Closely spaced horizontal closed ties (Fig 919)
help in three ways namely
(i) they carry the horizontal shear forces
induced by earthquakes and thereby resist
diagonal shear cracks
(ii) they hold together the vertical bars and
prevent them from excessively bending
outwards(in technical terms this bending
phenomenon is called buckling) and
(iii) they contain the concrete in the column
within the closed loops The ends of the
ties must be bent as 135deg hooks Such hook
ends prevent opening of loops and
consequently bulging of concrete and
buckling of vertical bars
Construction drawings with clear details of closed ties are helpful in the effective implementation
at construction site In columns where the spacing between the corner bars exceeds 300mm the
Indian Standard prescribes additional links with 180deg hook ends for ties to be effective in holding
the concrete in its place and to prevent the buckling of vertical bars These links need to go
around both vertical bars and horizontal closed ties (Fig 920) special care is required to
implement this properly at site
Designing a column involves selection of
materials to be used (ie grades of concrete and
steel bars) choosing shape and size of the cross-
section and calculating amount and distribution
of steel reinforcement The first two aspects are
part of the overall design strategy of the whole
building The IS 13920 1993 requires columns
to be at least 300mm wide A column width of up
to 200 mm is allowed if unsupported length is less
than 4m and beam length is less than 5m
Columns that are required to resist earthquake
forces must be designed to prevent shear failure
by a skillful selection of reinforcement
Fig 919 Steel reinforcement in columns ndash closed ties
at close spacing improve the performance of column
under strong earthquake shaking
Fig 920 Extra links are required to keep the
concrete in place ndash 180deg links are necessary to
prevent the135deg tie from bulging outwards
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913 एकसीयल लोिि मबसय क तलए सामानय आवशयकिाएा General Requirements for Axial
Loaded Members
These requirements apply to frame members which have a factored axial stress in excess of
01 fck under the effect of earthquake forces
The minimum dimension of the member shall not be less than 200 mm However in frames
which have beams with centre to centre span exceeding 5 m or columns of unsupported
length exceeding 4 m the shortest dimension of the column shall not be less than 300 mm
The ratio of the shortest cross sectional dimension to the perpendicular dimension shall
preferably not be less than 04
9131 अनदधयय सदढीकरण Longitudinal Reinforcement
Lap splices shall be provided only in the central half
of the member length It should be proportioned as a
tension splice Hoops shall be provided over the
entire splice length at spacing not exceeding 150
mm centre to centre Not more than 50 percent of
the bars shall be spliced at one section
Any area of a column that extends more than 100
mm beyond the confined core due to architectural
requirements shall be detailed in the following
manner
a) In case the contribution of this area to strength
has been considered then it will have the minimum longitudinal and transverse
reinforcement as per IS 13920 1993
b) However if this area has been treated as non-structural the minimum reinforcement
requirements shall be governed by IS 456 1978 provisions minimum longitudinal and
transverse reinforcement as per IS 456 1978 (as shown in Fig 921)
9132 अनपरसथ सदढीकरण Transverse Reinforcement
Transverse reinforcement for circular columns shall consist of spiral or circular hoops In
rectangular columns rectangular hoops may be used A rectangular hoop is a closed stirrup
having a 135deg hook with a 10 diameter extension (but not lt 75 mm) at each end that is
embedded in the confined core [as shown in (A) of Fig 922]
Fig 921 Reinforcement requirement for Column with more than 100 mm projection beyond core(IS 13920 1993)
Fig 922 Transverse Reinforcement in Column (IS 13920 1993)
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The parallel legs of rectangular hoop shall be spaced not more than 300 mm centre to centre
If the length of any side of the hoop exceeds 300 mm a crosstie shall be provided [as shown
in (B) of Fig 922] Alternatively a pair of overlapping hoops may be provided within the
column [as shown in (C) of Fig 922] The hooks shall engage peripheral longitudinal bars
The spacing of hoops shall not exceed half the least lateral dimension of the column except
where special confining reinforcement is provided as per Para 915 below
914 बीम-कॉलम जोड़ जो आर सी भवनो ो म भको प बलो ो का तवरोध करि ि Beam-Column Joints
that resist Earthquakes Forces in RC Buildings
In RC buildings portions of columns that are
common to beams at their intersections are
called beam column joints (Fig 923) The
joints have limited force carrying capacity
When forces larger than these are applied
during earthquakes joints are severely
damaged Repairing damaged joints is
difficult and so damage must be avoided
Thus beam-column joints must be designed
to resist earthquake effects
Under earthquake shaking the beams adjoining a joint are subjected to moments in the same
(clockwise or counter-clockwise) direction
Under these moments the top bars in the
beam-column joint are pulled in one
direction and the bottom ones in the
opposite direction These forces are
balanced by bond stress developed between
concrete and steel in the joint region
(Fig 924)
If the column is not wide enough or if the
strength of concrete in the joint is low there
is insufficient grip of concrete on the steel
bars In such circumstances the bar slips
inside the joint region and beams loose
their capacity to carry load Further under
the action of the above pull-push forces at top and bottom ends joints undergo geometric
distortion one diagonal length of the joint elongates and the other compresses
If the column cross-sectional size is insufficient the concrete in the joint develops diagonal
cracks
Fig 923 Beam-Column Joints are critical parts of a
building ndash they need to be designed
Fig924 Pull-push forces on joints cause two
problems ndash these result in irreparable damage in joints
under strong seismic shaking
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9141 बीम-कॉलम जोड़ मजबि करन क तलए सामानय आवशयकिाएा General Requirements
for Reinforcing the Beam-Column Joint
Diagonal cracking and crushing of concrete in joint
region should be prevented to ensure good
earthquake performance of RC frame buildings
(Fig 925)
Using large column sizes is the most effective
way of achieving this
In addition closely spaced closed-loop steel ties
are required around column bars to hold
together concrete in joint region and to resist
shear forces
Intermediate column bars also are effective in
confining the joint concrete and resisting
horizontal shear forces Providing closed-loop
ties in the joint requires some extra effort
IS 13920ndash1993 recommends continuing the
transverse loops around the column bars
through the joint region
In practice this is achieved by preparing the cage of
the reinforcement (both longitudinal bars and
stirrups) of all beams at a floor level to be prepared
on top of the beam formwork of that level and
lowered into the cage (Fig 926)
However this may not always be possible
particularly when the beams are long and the entire
reinforcement cage becomes heavy
The gripping of beam bars in the joint region is
improved first by using columns of reasonably
large cross-sectional size
The Indian Standard IS 13920-1993 requires building columns in seismic zones III IV and V to
be at least 300mm wide in each direction of the cross-section when they support beams that are
longer than 5m or when these columns are taller than 4m between floors (or beams)
In exterior joints where beams terminate at columns longitudinal beam bars need to be anchored
into the column to ensure proper gripping of bar in joint The length of anchorage for a bar of
grade Fe415 (characteristic tensile strength of 415MPa) is about 50 times its diameter This
Fig 925 Closed loop steel ties in beam-column
joints ndash such ties with 135deg hooks resist the ill
effects of distortion of joints
Fig 926 Providing horizontal ties in the joints ndash
three-stage procedure is required
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74
length is measured from the face of the column to the end of the bar anchored in the column
(Fig 927)
In columns of small widths and when beam
bars are of large diameter (Fig 928(a)) a
portion of beam top bar is embedded in the
column that is cast up to the soffit of the
beam and a part of it overhangs It is difficult
to hold such an overhanging beam top bar in
position while casting the column up to the
soffit of the beam Moreover the vertical
distance beyond the 90ordm bend in beam bars is
not very effective in providing anchorage
On the other hand if column width is large
beam bars may not extend below soffit of the
beam (Fig 928 (b)) Thus it is preferable to
have columns with sufficient width
In interior joints the beam bars (both top and
bottom) need to go through the joint without
any cut in the joint region Also these bars
must be placed within the column bars and
with no bends
915 तवशष सीतमि सदढीकरण Special Confining Reinforcement
This requirement shall be met with unless a
larger amount of transverse reinforcement is
required from shear strength considerations
Special confining reinforcement shall be
provided over a length lsquolorsquo from each
joint face towards mid span and on
either side of any section where flexural
yielding may occur under the effect of
earthquake forces (as shown in Fig 929)
The length lsquolorsquo shall not be less than
(a) larger lateral dimension of the
member at the section where yielding
occurs
(b) 16 of clear span of the member and
(c) 450 mm
Fig 929 Column and Joint Detailing (IS 13920 1993)
Fig 927 Anchorage of beam bars in exterior
joints ndash diagrams show elevation of joint region
Fig 928 Anchorage of beam bars in interior
jointsndash diagrams (a) and (b) show cross-sectional
views in plan of joint region
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When a column terminates into a footing or mat special confining reinforcement shall extend
at least 300 mm into the footing or mat (as shown in Fig 930)
When the calculated point of contra-flexure
under the effect of gravity and earthquake
loads is not within the middle half of the
member clear height special confining
reinforcement shall be provided over the full
height of the column
Columns supporting reactions from discontinued stiff members such as walls shall be
provided with special confining reinforcement over their full height (as shown in Fig 931)
This reinforcement shall also be placed above the discontinuity for at least the development
length of the largest longitudinal bar in the column Where the column is supported on a wall
this reinforcement shall be provided
over the full height of the column it
shall also be provided below the
discontinuity for the same development
length
Special confining reinforcement shall
be provided over the full height of a
column which has significant variation
in stiffness along its height This
variation in stiffness may result due to
the presence of bracing a mezzanine
floor or a RCC wall on either side of
the column that extends only over a part
of the column height (as shown in Fig
931)
916 तवशषिः भको पीय कषतर म किरनी दीवारो ो वाली इमारिो ो का तनमायण Construction of Buildings
with Shear Walls preferably in Seismic Regions
Reinforced concrete (RC) buildings often have vertical
plate-like RC walls called Shear Walls in addition to
slabs beams and columns These walls generally start
at foundation level and are continuous throughout the
building height Their thickness can be as low as
150mm or as high as 400mm in high rise buildings
Shear walls are usually provided along both length and
width of buildings Shear walls are like vertically-
oriented wide beams that carry earthquake loads
downwards to the foundation (Fig 932)
Fig 932 Reinforced concrete shear walls in
buildings ndash an excellent structural system for
earthquake resistance
Fig 930 Provision of Special confining reinforcement in Footings (IS 13920 1993)
Fig 931 Special Confining Reinforcement Requirement for
Columns under Discontinued Walls (IS 13920 1993)
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76
Properly designed and detailed buildings with shear walls have shown very good performance in
past earthquakes Shear walls in high seismic regions require special detailing Shear walls are
efficient both in terms of construction cost and effectiveness in minimizing earthquake damage
in structural and non-structural elements (like glass windows and building contents)
Shear walls provide large strength and
stiffness to buildings in the direction of their
orientation which significantly reduces lateral
sway of the building and thereby reduces
damage to structure and its contents
Since shear walls carry large horizontal
earthquake forces the overturning effects on
them are large Thus design of their
foundations requires special attention
Shear walls should be provided along
preferably both length and width However if
they are provided along only one direction a
proper grid of beams and columns in the
vertical plane (called a moment-resistant
frame) must be provided along the other
direction to resist strong earthquake effects
Door or window openings can be provided in shear walls but their size must be small to
ensure least interruption to force flow through walls
Shear walls in buildings must be symmetrically located in plan to reduce ill-effects of twist in
buildings (Fig 933)
Shear walls are more effective when located along exterior perimeter of the building ndash such a
layout increases resistance of the building to twisting
9161 िनय तिजाइन और किरनी दीवारो ो की जयातमति Ductile Design and Geometry of Shear
Walls
Shear walls are oblong in cross-section ie one dimension of the cross-section is much larger
than the other While rectangular cross-section is common L- and U-shaped sections are also
used Overall geometric proportions of the wall types and amount of reinforcement and
connection with remaining elements in the building help in improving the ductility of walls The
Indian Standard Ductile Detailing Code for RC members (IS13920-1993) provides special
design guidelines for ductile detailing of shear walls
917 इमपरवड़ तिजाइन रणनीतियाो Improved design strategies
9171 िातनकारक भको प परभाव स भवनो ो का सोरकषण Protection of Buildings from Damaging
Earthquake Effects
Conventional seismic design attempts to make buildings that do not collapse under strong
earthquake shaking but may sustain damage to non-structural elements (like glass facades) and
to some structural members in the building There are two basic technologies ndashBase Isolation
Fig 933 Shear walls must be symmetric in plan
layout ndash twist in buildings can be avoided
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Devices and Seismic Dampers which are used to protect buildings from damaging earthquake
effects
9172 आधार अलगाव Base Isolation
The idea behind base isolation is to detach (isolate) the building from the ground in such a way
that earthquake motions are not transmitted up through the building or at least greatly reduced
As illustrated in Fig 934 when the ground shakes the rollers freely roll but the building
above does not move Thus no force is
transferred to the building due to shaking of
the ground simply the building does not
experience the earthquake
As illustrated in Fig 935 if the same
building is rested on flexible pads that offer
resistance against lateral movements then
some effect of the ground shaking will be
transferred to the building above
As illustrated in Fig 936 if the flexible
pads are properly chosen the forces induced
by ground shaking can be a few times
smaller than that experienced by the
building built directly on ground namely a
fixed base building
9173 भको पी सोज Seismic Dampers
Seismic dampers are special devices introduced in the building to absorb the energy provided by
the ground motion to the building These dampers act like the hydraulic shock absorbers in cars ndash
much of the sudden jerks are absorbed in the hydraulic fluids and only little is transmitted above
to the chassis of the car
When seismic energy is transmitted through them dampers absorb part of it and thus damp the
motion of the building Commonly used types of seismic dampers (Fig 937) include
Fig 934 Hypothetical Building
Fig 935 Base Isolated Building
Fig 936 Fixed-Base Building
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Viscous dampers ndash Energy is absorbed by
silicone-based fluid passing between piston-
cylinder arrangement
Friction dampers ndash Energy is absorbed by
surfaces with friction between them rubbing
against each other
Yielding dampers ndash Energy is absorbed by
metallic components that yield
In India friction dampers have been provided in an
18-storey RC frame structure in Gurgaon
918 तिजाइन उदािरण Design Example ndash Beam Design of RC Frame with Ductile
Detailing
Exercise ndash 2 Beam Design of RC Frame Building as per Provision of IS 13920 1993 and IS
1893 (Part 1) 2002 Beam marked ABC is considered for Design
Fig 937 Seismic Energy Dissipation Devices
each device is suitable for a certain building
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79
ELEVATION
Solution
1 General Data Grade of Concrete = M 25
Grade of steel = Fe 415 Tor Steel
2 Load Combinations
As per Cl 63 of IS 1893 (Part 1) 2002 following are load combinations for Earthquake
Loading
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S No Load Combination DL LL EQ Remark
1 15 DL + 15 LL 15 15 ndash As per Table ndash 8
of IS 1893 (Part
1) 2002 2 12 (DL + LL
+ EQx) 15 025 or 050 +12
3 12 (DL + LL ndash EQx) 15 025 or 050 ndash12
4 12 (DL + LL + EQy) 15 025 or 050 +12
5 12 (DL + LL ndash EQy) 15 025 or 050 ndash12
6 15 (DL + EQx) 15 +15
7 15 (DL ndash EQx) 15 ndash15
8 15 (DL + EQy) 15 +15
9 15 (DL ndash EQy) 15 ndash15
10 09 DL + 15 EQx 15 +15
11 09 DL ndash 15 EQx 15 ndash15
12 09 DL + 15 EQy 15 +15
13 09 DL ndash 15 EQy 15 ndash15
EQx implies EQ Loading in X ndash direction amp EQy implies EQ Loading in Y ndash direction
where X amp Y are orthogonal directions and Z is vertical direction These load combinations
are for EQ Loading In practice Wind Load should also be considered in lieu of EQ Load
and critical of the two should be used in the design
In this exercise emphasis is to show calculations for ductile design amp detailing of building
elements subjected to Earthquake in the plan considered Beams parallel to Y ndash direction are
not significantly affected by Earthquake force in X ndash direction (except in case of highly
unsymmetrical building) and vice versa Beams parallel to Y ndash direction are designed for
Earthquake loading in Y ndash direction only
Torsion effect is not considered in this example
3 Force Data
For Beam AB force resultants for various load cases (ie DL LL amp EQ Load) from
Computer Analysis (or manually by any method of analysis) to illustrate the procedure of
design are tabulated below
Table ndash A Force resultants in beam AB for various load cases
Load Case Left End Centre Right End
Shear
(KN)
Moment
(KN-m)
Shear
(KN)
Moment
(KN-m)
Shear
(KN)
Moment
(KN-m)
DL ndash 51 ndash 37 4 32 59 ndash 56
LL ndash 14 ndash 12 1 11 16 ndash 16
EQY 79 209 79 11 79 ndash 119
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Table ndash B Force resultants in beam AB for different load combinations
Load Combinations Left End Centre Right End
Shear
(KN)
Moment
(KN-m)
Shear
(KN)
Moment
(KN-m)
Shear
(KN)
Moment
(KN-m)
15 DL + 15 LL 98 ndash 74 7 64 111 ndash 108
12 (DL + LL + EQy) 31 205 101 52 172 ndash 303
12 (DL + LL ndash EQy) 162 ndash 300 92 31 22 159
15 (DL + EQy) 44 261 127 61 209 ndash 372
15 (DL ndash EQy) 97 ndash 371 115 34 33 205
09 DL + 15 EQy 75 283 124 42 174 ndash 339
09 DL ndash 15 EQy 167 ndash 349 117 15 68 238
4 Various checks for Flexure Member
(i) Check for Axial Stress
As per Cl 611 of IS 13920 1993 flexural axial stress on the member under EQ loading
shall not exceed 01 fck
Factored Axial Force = 000 KN
Factored Axial Stress = 000 MPa lt 010 fck OK
Hence the member is to be designed as Flexure Member
(ii) Check for Member size
As per Cl 613 of IS 13920 1993 width of the member shall not be less than 200 mm
Width of the Beam B = 250 mm gt 200 mm OK
Depth of Beam D = 550 mm
As per Cl 612 member shall have a width to depth ratio of more than 03
BD = 250550 = 04545 gt 03 OK
As per Cl 614 depth of member shall preferably be not more than 14 of the clear span
ie (DL) lt 14 or (LD) gt4
Span = 4 m LD = 4000550 = 727 gt 4 OK
Check for Limiting Longitudinal Reinforcement
Nominal cover to meet Durability requirements as per = 30 mm
Table ndash 16 of IS 4562000 (Cl 2642) for Moderate Exposure
Effective depth for Moderate Exposure conditions = 550 ndash 30 ndash 20 ndash (202)
with 20 mm of bars in two layers = 490 mm
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82
As per Cl 621 (b) of IS 13920 1993 tension steel ratio on any face at any section shall not
be less than = (024 radic fck) fy
= (024 radic25) 415 = 0289 asymp 029
Min Reinforcement = (029100) X 250 X 490 = 356 mm2
Max Reinforcement 25 = (25100) X 250 X 490 = 3063 mm2
(iii) Design for Flexure
Design for Hogging Moment at support A
At end A from Table ndash B Mu = 371 KN-m
Therefore Mu bd2 = 371x10
6 (250 x 490 x 490) = 618
Referring to Table ndash 51 of SP ndash 16 for drsquod = 55490 = 011
We get Ast at top = 2013 Asc = 0866
Therefore Ast at top = (2013100) x 250 x 490
= 2466 mm2
gt 356 mm2 (Min Reinforcement)
lt 3063 mm2 (Max Reinforcement)
Asc at bottom = 0866
As per Cl 623 of IS 13290 1993 positive steel at a joint face must be at least equal to half
the ndashve steel at that face Therefore Asc at bottom must be at least 50 of Ast hence
Revised Asc = 20132 = 10065
Asc at bottom = (10065100) x 250 x 490
= 1233 mm2 gt 426 mm
2 (Min Reinforcement)
lt 3063 mm2 (Max Reinforcement)
Design for Sagging Moment at support A
Mu = 283 KN-m
The beam will be designed as T-beam The limiting capacity of the T-beam assuming xu lt Df
and xu lt xumax may be calculated as follows
Mu = 087 fy Ast d [1- (Ast fy bf d fck)] -------- (Eq ndash 1)
Where Df = Depth of Flange
= 150 mm
xu = Depth of Neutral Axis
xumax = Limiting value of Neutral Axis
= 048 d
= 048 X 490
= 23520 mm
bw = 250 mm
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83
bf = Width of Flange
= (L06) + bw + 6 Df or cc of beam
= (07 X 40006) + 250 + 6 X 150
= 467 + 250 + 900 = 1617 mm or 4000 mm cc
[Lower of two is to be adopted]
Substituting the values in Eq ndash 1 and solving the quadratic equation
283 X 106 = 087 X 415 Ast X 490 [1ndash (Ast X 415) (1617 X 490 X 25)]
= 1769145 Ast [1 ndash 2095 X 10-5
Ast]
283 X 106 = 1769145 Ast ndash 3706 Ast
2]
3706 Ast2 ndash 1769145 Ast + 283 X 10
6 = 0
Ast = [1769145 plusmn radic(17691452 ndash 4 X 3706 X 283 X 10
6)] 2 X 3706
= [1769145 plusmn radic(3129874 X 1010
ndash 4195192 X 106)] 2 X 3706
= (1769145 plusmn 16463155) 7412
Ast at bottom = 165717 mm2 gt 35600 mm
2
lt 306300 mm2 OK
It is necessary to check the design assumptions before finalizing the reinforcement
xu = (087 fy Ast) (036 fck bf)
= (087 X 415 X 1657) (036 X 25 X 1617)
= 4110 mm lt 150 mm OK
lt df
lt xumax = 048 X 490 = 235 mm OK
Ast = [1657(250X490)] X 100 = 1353
As per Cl 624 ldquoSteel provided at each of the top amp bottom face of the member at any one
section along its length shall be at least equal to 14th
of the maximum (-ve) moment steel
provided at the face of either joint
For Centre Mu = 64 KN-m
64 X 106 = 087 X 415 Ast X 490 [1ndash (Ast X 415) (1617 X 490 X 25)]
= 1769145 Ast [1 ndash 2095 X 10-5
Ast]
64 X 106 = 1769145 Ast ndash 3706 Ast
2]
3706 Ast2 ndash 1769145 Ast + 64 X 10
6 = 0
Ast = [1769145 plusmn radic(17691452 ndash 4 X 3706 X 64 X 10
6)] 2 X 3706
= 365 mm2
For Right Support Mu = 238 KN-m
238 X 106 = 087 X 415 Ast X 490 [1ndash (Ast X 415) (1617 X 490 X 25)]
= 1769145 Ast [1 ndash 2095 X 10-5
Ast]
238 X 106 = 1769145 Ast ndash 3706 Ast
2]
3706 Ast2 ndash 1769145 Ast + 238 X 10
6 = 0
Ast = [1769145 plusmn radic(17691452 ndash 4 X 3706 X 238 X 10
6)] 2 X 3706
= 1386 mm2
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84
(iv) Reinforcement Requirement
Top reinforcement is larger of Ast at top for hogging moment or Asc at top for sagging
moment ie 2466 mm2 or 968 mm
2 Hence provide 2466 mm
2 at top
Bottom reinforcement is larger of Asc at bottom for hogging moment or Ast at bottom for
sagging moment ie 1233 mm2 or 1936 mm
2 Hence provide 1936 mm
2 at bottom
Details of Reinforcement
Top Reinforcement
Beam AB Left End Centre Right End
Hogging Moment ndash 371 - ndash 371
Mu bd2 618 - 618
Ast at top 2013 - 2013
Asc at bottom 0866 lt 2013 2 =
10065 Hence
revised Asc = 10065
- 0866
Revised to
10065 as per Cl
623 of IS
139201993
Bottom Reinforcement
Sagging Moment 283 64 238
Ast at bottom Ast req = 1657 mm2
= 1353
gt 20132 =
10065 OK
Provide Ast at bottom
= 1353
Ast req = 365 mm2
= 0298
gt 029
gt 20134 =
0504 OK
As per Cl 624 of IS
139201993
Provide Ast at bottom
= 0504
Ast req = 1386 mm2
= 117
gt 029
gt 20132 =
10065
Provide Ast at
bottom = 117
Asc at top Asc req = 1657 2
= 829 mm2
= 0677
gt 029
gt 2013 4 =
0504 OK
Asc req = 05042
= 0252
gt 029 Provide MinAsc = 029
Asc req = 1657 2
= 829 mm2
= 0677
gt 029
gt 2013 4
= 0504
OK
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85
Summary of Reinforcement required
Beam Left End Centre Right End
Top = 2013
= 2466 mm2
Bottom = 1353
= 1658 mm2
Top = 0504
= 618 mm2
Bottom = 0504
= 618 mm2
Top = 2013
= 2466 mm2
Bottom = 10065
= 1233 mm2
Reinforcement provided
2 ndash 20Φ cont + 4 ndash 25Φ extra
Ast = 2592 mm2 (2116)
2 ndash 20Φ cont + 2 ndash 20Φ extra
+ 2 ndash 16 Φ
Ast = 1658 mm2 (1353)
2 ndash 20Φ cont
Ast = 628 mm2 (0512)
2 ndash 20Φ cont
Ast = 628 mm2 (0512)
2 ndash 20Φ cont
+ 4 ndash 25Φ extra
Top = 2592 mm2
2 ndash 20Φ cont
+ 2 ndash 20Φ extra + 2 ndash 16Φ
Ast = 1658 mm2 (1353)
Details of Reinforcement
Ld = Development Length in tension
db = Dia of bar
For Fe 415 steel and M25 grade concrete as per Table ndash 65 of SP ndash 16
For 25Φ bars 1007 + 10Φ - 8Φ = 1007+50 = 1057 mm
For 20Φ bars 806 + 2Φ = 806+40 = 846 mm
(v) Design for Shear
Tensile steel provided at Left End = 2116
Permissible Design Stress of Concrete
(As per Table ndash 19 of IS 4562000) τc = 0835 MPa
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Design Shear Strength of Concrete = τc b d
= (0835 X 250 X 490) 1000
= 102 KN
Similarly Design Shear Strength of Concrete at centre for Ast = 0512
τc = 0493 MPa
Shear Strength of Concrete at centre = τc b d
= (0493 X 250 X 490) 1000
= 6040 KN
(vi) Shear force due to Plastic Hinge Formation at the ends of the beam
The additional shear due to formation of plastic hinges at both ends of the beams is evaluated
as per Cl 633 of IS 139201993 is given by
Vsway to right = plusmn 14 [MulimAs
+ MulimBh
] L
Vsway to left = plusmn 14 [MulimAh
+ MulimBs
] L
Where
MulimAs
= Sagging Ultimate Moment of Resistance of Beam Section at End A
MulimAh
= Hogging Ultimate Moment of Resistance of Beam Section at End A
MulimBh
= Sagging Ultimate Moment of Resistance of Beam Section at End B
MulimBs
= Hogging Ultimate Moment of Resistance of Beam Section at End B
At Ends beam is provided with steel ndash pt = 2116 pc = 1058
Referring Table 51 of SP ndash 16 for pt = 2116 pc = 1058
The lowest value of MuAh
bd2 is found
MuAh
bd2 = 645
Hogging Moment Capacity at End A
MuAh
= 645 X 250 X 4902
= 38716 X 108 N-mm
= 38716 KN-m
Similarly for MuAs
pt = 1058 pc = 2116
Contribution of Compressive steel is ignored while calculating the Sagging Moment
Capacity at T-beam
MuAs
= 087 fy Ast d [1- (Ast fy bf d fck)]
= 087 X 415 X 1658 X 490 [1ndash (1658 X 415 1617 X 490 X 25)]
= 28313 KN-m
Similarly for Right End of beam
MuBh
= 38716 KN-m amp MuBs
= 28313 KN-m
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87
Shear due to Plastic Hinge is calculated as
Vsway to right = plusmn 14 [MuAs
+ MuBh
] L
= plusmn 14 [28313 + 38716] 4
= 23460 KN
Vsway to left = plusmn 14 [MuAh
+ MuBs
] L
= plusmn 14 [38716 + 28313] 4
= 23460 KN
Design Shear
Dead Load of Slab = 50 KNm2 Live Load = 40 KNm
2
Load due to Slab in Beam AB = 2 X [12 X 4 X 2] X 5 = 40 KN (10 KNm)
Self Wt Of Beam = 025 X 055 X 25 X 4 = 1375 KN (344 KNm)
asymp 1400 KN
Live Load = 2 X [12 X 4 X 2] X 4 = 32 KN (8 KNm)
Shear Force due to DL = 12 X [40 + 14] = 27 KN
Shear Force due to LL = 12 X [32] = 16 KN
As per Cl 633 of IS 139201993 the Design shear at End A ie Vua and Design Shear at
End B ie Vub are computed as
(i) For Sway Right
Vua = VaD+L
ndash 14 [MulimAs
+ MulimBh
] LAB
Vub = VbD+L
+ 14 [MulimAs
+ MulimBh
] LAB
(ii) For Sway Left
Vua = VaD+L
+ 14 [MulimAh
+ MulimBs
] LAB
Vub = VbD+L
ndash 14 [MulimAh
+ MulimBs
] LAB
Where
VaD+L
amp VbD+L
= Shear at ends A amp B respectively due to vertical load with
Partial Safety Factor of 12 on Loads
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VaD+L
= VbD+L
= 12 (D+L) 2
--------------For equ (i)
---------------For equ (ii)
14 X [MuAs
+ MuBh
] L = 23460 KN
14 X [MuAh
+ MuBs
] L = 23460 KN
VaD = Vb
D = 12 X 27 = 324
= 516
VaL = Vb
L = 12 X 16 = 192
Vua = [12 (27+16)] ndash 23460 = 516 ndash 23460 = (-) 18300 KN
Vub = [12 (27+16)] + 23460 = 516 + 23460 = (+) 28620 KN
Vub = [12 (27+16)] + 23460 = 516 + 23460 = (+) 28620 KN
Vua = [12 (27+16)] ndash 23460 = 516 ndash 23460 = (-) 18300 KN
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As per Cl 633 of IS 139201993 the Design Shear Force to be resisted shall be of
maximum of
(i) Calculate factored SF as per analysis ( Refer Table ndash B)
(ii) Shear Force due to formation of Plastic Hinges at both ends of the beam plus
factored gravity load on the span
Hence Design shear Force Vu will be 28620 KN (corresponding to formation of Plastic
Hinge)
From Analysis as per Table ndash B SF at mid-span of the beam is 127 KN However Shear
due to formation of Plastic Hinge is 23460 KN Hence design shear at centre of span is
taken as 23460 KN
The required capacity of shear reinforcement at ends
Vus = Vu - Vc
= 28620 ndash 102
= 18420 KN
And at centre Vus = 23460 ndash 6040
= 17420 KN
At supports
Vus d = 28620 49 = 584 KNcm
Therefore requirement of stirrups is
12Φ ndash 2 legged strippus 135 cc [Vus d = 606]
However provide 12Φ ndash 2 legged strippus 120 cc as per provision of Cl 635 of IS
139201993 [Vus d = 6806]
At centre
Vus d = 23460 49 = 478 KNcm
Provide 12Φ ndash 2 legged strippus 170 cc [Vus d = 4804]
As per Cl 635 of IS 139201993 the spacing of stirrups in the mid-span should not
exceed d2 = 4902 = 245 mm
Minimum Shear Reinforcement as per Cl 26516 of IS 4562000 is
Sv = Asv X 08 fy 046
= (2 X 79 X 087 X 415) (250 X 04)
= 570 mm
As per CL 635 of IS 139201993 ldquoSpacing of Links over a length of 2d at either end of
beam shall not exceed
(i) d4 = 4904 = 12250 mm
(ii) 8 times dia of smallest longitudinal bar = 8 X 16 = 128 mm
However it need not be less than 100 mm
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The reinforcement detailing is shown as below
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अधयाय Chapter ndash 10
अलप सामरथय तचनाई सोरचनाओो क तनमायण Construction of Low Strength Masonry Structures
Two types of construction are included herein namely
a) Brick construction using weak mortar and
b) Random rubble and half-dressed stone masonry construction using different mortars such as
clay mud lime-sand and cement sand
101 भको प क दौरान ईोट तचनाई की दीवारो ो का वयविार Behaviour of Brick Masonry Walls
during Earthquakes
Of the three components of a masonry building (roof wall and foundation as illustrated in
Fig101) the walls are most vulnerable to damage caused by horizontal forces due to earthquake
Ground vibrations during earthquakes cause inertia forces at locations of mass in the building (Fig 102) These forces travel through the roof and walls to the foundation The main emphasis
is on ensuring that these forces reach the ground without causing major damage or collapse
A wall topples down easily if pushed
horizontally at the top in a direction
perpendicular to its plane (termed weak
Fig 101 Basic components of Masonry Building
Fig 103 For the direction of Earthquake shaking
shown wall B tends to fail
at its base
Fig 102 Effect of Inertia in a building when shaken
at its base
Fig 104 Direction of force on a wall critically determines
its earthquake performance
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direction) but offers much greater resistance if pushed along its length (termed strong direction) (Fig 103 amp 104)
The ground shakes simultaneously in the vertical and two horizontal directions during
earthquakes However the horizontal vibrations are the most damaging to normal masonry
buildings Horizontal inertia force developed at the
roof transfers to the walls acting either in the weak
or in the strong direction If all the walls are not tied
together like a box the walls loaded in their weak
direction tend to topple
To ensure good seismic performance all walls must
be joined properly to the adjacent walls In this way
walls loaded in their weak direction can take
advantage of the good lateral resistance offered by
walls loaded in their strong direction (Fig 105)
Further walls also need to be tied to the roof and
foundation to preserve their overall integrity
102 तचनाई वाली इमारिो ो म बॉकस एकशन कस सतनतिि कर How to ensure Box Action in
Masonry Buildings
A simple way of making these walls behave well during earthquake shaking is by making them
act together as a box along with the roof at the top and with the foundation at the bottom A
number of construction aspects are required to ensure this box action
Firstly connections between the walls should be good This can be achieved by (a) ensuring
good interlocking of the masonry courses at the junctions and (b) employing horizontal bands
at various levels particularly at the lintel level
Secondly the sizes of door and window
openings need to be kept small The smaller
the opening the larger is the resistance
offered by the wall
Thirdly the tendency of a wall to topple
when pushed in the weak direction can be
reduced by limiting its length-to-thickness
and height to-thickness ratios Design codes
specify limits for these ratios A wall that is
too tall or too long in comparison to its
thickness is particularly vulnerable to
shaking in its weak direction (Fig 106)
Fig 106 Slender walls are vulnerable
Fig 105 Wall B properly connected to Wall A
(Note roof is not shown) Walls A
(loaded in strong direction) support
Walls B (loaded in weak direction)
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Brick masonry buildings have large mass and hence attract large horizontal forces during
earthquake shaking They develop numerous cracks under both compressive and tensile forces
caused by earthquake shaking The focus of earthquake resistant masonry building construction
is to ensure that these effects are sustained without major damage or collapse Appropriate choice
of structural configuration can help achieve this
The structural configuration of masonry buildings
includes aspects like (a) overall shape and size of the
building and (b) distribution of mass and
(horizontal) lateral load resisting elements across the
building
Large tall long and un-symmetric buildings perform
poorly during earthquakes A strategy used in making
them earthquake resistant is developing good box
action between all the elements of the building ie
between roof walls and foundation (Fig 107) For
example a horizontal band introduced at the lintel
level ties the walls together and helps to make them
behave as a single unit
103 कषतिज बि की भतमका Role of Horizontal Bands
Horizontal bands are the most important
earthquake-resistant feature in masonry
buildings The bands are provided to hold a
masonry building as a single unit by tying all
the walls together and are similar to a closed
belt provided around cardboard boxes
(Fig 108 amp 109)
The lintel band undergoes bending and pulling actions during earthquake shaking
(Fig1010)
To resist these actions the construction of lintel band requires special attention
Fig 107 Essential requirements to ensure
box action in a masonry building
Fig 108 Building with flat roof
Fig 109 Two-storey Building with pitched roof
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Bands can be made of wood (including bamboo splits) or of reinforced concrete (RC) the
RC bands are the best (Fig 1011)
The straight lengths of the band must be properly connected at the wall corners
In wooden bands proper nailing of straight lengths with spacers is important
In RC bands adequate anchoring of steel links with steel bars is necessary
The lintel band is the most important of all and needs to be provided in almost all buildings
The gable band is employed only in buildings with pitched or sloped roofs
In buildings with flat reinforced concrete or reinforced brick roofs the roof band is not
required because the roof slab also plays the role of a band However in buildings with flat
timber or CGI sheet roof roof band needs to be provided In buildings with pitched or sloped
roof the roof band is very important
Plinth bands are primarily used when there is concern about uneven settlement of foundation
soil
Lintel band Lintel band is a band provided at lintel level on all load bearing internal external
longitudinal and cross walls
Roof band Roof band is a band provided immediately below the roof or floors Such a band
need not be provided underneath reinforced concrete or brick-work slabs resting on bearing
Fig 1010 Bending and pulling in lintel bands ndash Bands must be capable of resisting these actions
Fig 1011 Horizontal Bands in masonry buildings ndash RC bands are the best
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walls provided that the slabs are continuous over the intermediate wall up to the crumple
sections if any and cover the width of end walls fully or at least 34 of the wall thickness
Gable band Gable band is a band provided at the top of gable masonry below the purlins This
band shall be made continuous with the roof band at the eaves level
Plinth band Plinth band is a band provided at plinth level of walls on top of the foundation
wall This is to be provided where strip footings of masonry (other than reinforced concrete or
reinforced masonry) are used and the soil is either soft or uneven in its properties as frequently
happens in hill tracts This band will serve as damp proof course as well
104 अधोलोब सदढीकरण Vertical Reinforcement
Vertical steel at corners and junctions of walls which are up to 340 mm (1frac12 brick) thick shall be
provided as specified in Table 101 For walls thicker than 340 mm the area of the bars shall be
proportionately increased
No vertical steel need be provided in category A building The vertical reinforcement shall be
properly embedded in the plinth masonry of foundations and roof slab or roof band so as to
develop its tensile strength in bond It shall be passing through the lintel bands and floor slabs or
floor level bands in all storeys
Table ndash 101 Vertical Steel Reinforcement in Masonry Walls with Rectangular Masonry Units (IS 4326 1993)
No of Storeys Storey Diameter of HSD Single Bar in mm at Each Critical Section
Category B Category C Category D Category E One mdash Nil Nil 10 12
Two Top
Bottom
Nil
Nil
Nil
Nil
10
12
12
16
Three Top
Middle
Bottom
Nil
Nil
Nil
10
10
12
10
12
12
12
16
16
Four Top
Third
Second
Bottom
10
10
10
12
10
10
12
12
10
12
16
20
Four storeyed
building not
permitted
NOTES
1 The diameters given above are for HSD bars For mild-steel plain bars use equivalent diameters as given under
Table ndash 106 Note 2
2 The vertical bars will be covered with concrete M15 or mortar 1 3 grade in suitably created pockets around the
bars This will ensure their safety from corrosion and good bond with masonry
3 In case of floorsroofs with small precast components also refer 923 of IS 4326 1993 for floorroof band details
Bars in different storeys may be welded (IS 2751 1979 and IS 9417 1989 as relevant) or
suitably lapped
Vertical reinforcement at jambs of window and door openings shall be provided as per
Table ndash 101 It may start from foundation of floor and terminate in lintel band (Fig 1017)
Typical details of providing vertical steel in brickwork masonry with rectangular solid units
at corners and T-junctions are shown in Fig 1012
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105 दीवारो ो म सराखो ो का सोरकषण Protection of Openings in Walls
Horizontal bands including plinth band lintel band and roof band are provided in masonry
buildings to improve their earthquake performance Even if horizontal bands are provided
masonry buildings are weakened by the openings in their walls
Embedding vertical reinforcement bars in the edges of the wall piers and anchoring them in the
foundation at the bottom and in the roof band at the top forces the slender masonry piers to
undergo bending instead of rocking In wider wall piers the vertical bars enhance their capability
to resist horizontal earthquake forces and delay the X-cracking Adequate cross-sectional area of
these vertical bars prevents the bar from yielding in tension Further the vertical bars also help
protect the wall from sliding as well as from collapsing in the weak direction
However the most common damage observed after an earthquake is diagonal X-cracking of
wall piers and also inclined cracks at the corners of door and window openings
When a wall with an opening deforms during earthquake shaking the shape of the opening
distorts and becomes more like a rhombus - two opposite corners move away and the other two
come closer Under this type of deformation the corners that come closer develop cracks The
cracks are bigger when the opening sizes are larger Steel bars provided in the wall masonry all
Fig 1012 Typical Details of Providing Vertical Steel Bars in Brick Masonry (IS 4326 1993)
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around the openings restrict these cracks at the corners In summary lintel and sill bands above
and below openings and vertical reinforcement adjacent to vertical edges provide protection
against this type of damage (Fig 1013)
106 भको प परतिरोधी ईोट तचनाई भवन क तनमायण िि सामानय तसदाोि General Principles for
Construction of Earthquake Resistant Brick Masonry Building
Low Strength Masonry constructions should not be permitted for important buildings
It will be useful to provide damp-proof course at plinth level to stop the rise of pore water
into the superstructure
Precautions should be taken to keep the rain water away from soaking into the wall so that
the mortar is not softened due to wetness An effective way is to take out roof projections
beyond the walls by about 500 mm
Use of a water-proof plaster on outside face of walls will enhance the life of the building and
maintain its strength at the time of earthquake as well
Ignoring tensile strength free standing walls should be checked against overturning under the
action of design seismic coefficient ah allowing for a factor of safety of 15
1061 भवनो ो की शरतणयाा Categories of Buildings
For the purpose of specifying the earthquake resistant features in masonry and wooden buildings
the buildings have been categorized in five categories A to E based on the seismic zone and the
importance of building I
Where
I = importance factor applicable to the
building [Ref Clause 642 and
Table - 6 of IS 1893 (Part 1) 2002]
The building categories are given in
Table ndash 102
Fig 1013 Cracks at corners of openings in a masonry building ndash reinforcement around them helps
Table -102 Building Categories for Earthquake Resisting Features (IS 4326 1993)
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1062 कमजोर गार म ईोट तचनाई कायय Brickwork in Weak Mortars
The fired bricks should have a compressive strength not less than 35 MPa Strength of bricks
and wall thickness should he selected for the total building height
The mortar should be lime-sand (13) or clay mud of good quality Where horizontal steel is
used between courses cement-sand mortar (13) should be used with thickness so as to cover
the steel with 6 mm mortar above and below it Where vertical steel is used the surrounding
brickwork of 1 X 1 or lfrac12 X 1frac12 brick size depending on wall thickness should preferably be
built using 16 cement-sand mortar
The minimum wall thickness shall be one brick in one storey construction and one brick in
top storey and 1frac12brick in bottom storeys of up to three storey constructions It should also
not be less than l16 of the length of wall between two consecutive perpendicular walls
The height of the building shall be restricted to the following where each storey height shall
not exceed 30 m
For Categories A B and C - three storeys with flat roof and two storeys plus attic pitched
roof
For Category D - two storeys with flat roof and one storey plus attic for pitched roof
1063 आयिाकार तचनाई इकाइयो ो वाला तचनाई तनमायण Masonry Construction with
Rectangular Masonry Units
General requirements for construction of masonry walls using rectangular masonry units are
10631 तचनाई इकाइयाो Masonry Units
Well burnt bricks conforming to IS 1077 1992 or solid concrete blocks conforming to IS
2185 (Part 1) 1979 and having a crushing strength not less than 35 MPa shall be used The
strength of masonry unit required
shall depend on the number of storeys
and thickness of walls
Squared stone masonry stone block
masonry or hollow concrete block
masonry as specified in IS 1597 (Part
2) 1992 of adequate strength may
also be used
10632 गारा Mortar
Mortars such as those given in Table
ndash 103 or of equivalent specification
shall preferably be used for masonry
Table ndash 103 Recommended Mortar Mixes (IS 4326 1993)
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construction for various categories of buildings
Where steel reinforcing bars are provided in masonry the bars shall be embedded with
adequate cover in cement sand mortar not leaner than 13 (minimum clear cover 10 mm) or in
cement concrete of grade M15 (minimum clear cover 15 mm or bar diameter whichever
more) so as to achieve good bond and corrosion resistance
1064 दीवार Walls
Masonry bearing walls built in mortar as specified in 10632 above unless rationally
designed as reinforced masonry shall not be built of greater height than 15 m subject to a
maximum of four storeys when measured from the mean ground level to the roof slab or
ridge level
The bearing walls in both directions shall be straight and symmetrical in plan as far as
possible
The wall panels formed between cross walls and floors or roof shall be checked for their
strength in bending as a plate or as a vertical strip subjected to the earthquake force acting on
its own mass
Note mdash For panel walls of 200 mm or larger thickness having a storey height not more than
35 metres and laterally supported at the top this check need not be exercised
1065 तचनाई बॉणड Masonry Bond
For achieving full strength of
masonry the usual bonds
specified for masonry should be
followed so that the vertical joints
are broken properly from course
to course To obtain full bond
between perpendicular walls it is
necessary to make a slopping
(stepped) joint by making the
corners first to a height of 600
mm and then building the wall in
between them Otherwise the
toothed joint (as shown in Fig
1014) should be made in both the
walls alternatively in lifts of
about 450 mm
Panel or filler walls in framed buildings shall be properly bonded to surrounding framing
members by means of suitable mortar (as given in 10632 above) or connected through
dowels
Fig 1014 Alternating Toothed Joints in Walls at Corner and T-Junction (IS 4326 1993)
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107 ओपतनोग का परभाव Influence of Openings
Openings are functional necessities in buildings
During earthquake shaking inertia forces act in
the strong direction of some walls and in the weak
direction of others Walls shaken in the weak
direction seek support from the other walls ie
walls B1 and B2 seek support from walls A1 and
A2 for shaking in the direction To be more
specific wall B1 pulls walls A1 and A2 while
wall B2 pushes against them
Thus walls transfer loads to each other at their
junctions (and through the lintel bands and roof)
Hence the masonry courses from the walls
meeting at corners must have good interlocking
(Fig 1015) For this reason openings near the
wall corners are detrimental to good seismic
performance Openings too close to wall corners
hamper the flow of forces from one wall to
another Further large openings weaken walls
from carrying the inertia forces in their own
plane Thus it is best to keep all openings as small as possible and as far away from the corners
as possible
108 धारक दीवारो ो म ओपतनोग परदाि करि की सामानय आवशयकताए General Requirements of
Providing Openings in Bearing Walls
Door and window openings in walls reduce their lateral load resistance and hence should
preferably be small and more centrally located The guidelines on the size and position of
opening are given in Table ndash 104 and in Fig 1016
Fig 1015 Regions of force transfer from weak
walls to strong walls in a masonry building ndash Wall
B1 pulls walls A1 and A2 while wall B2pushes walls
A1 and A2
Fig 1016 Dimensions of Openings and Piers for
Recommendations in Table 3 (IS 4326 1993)
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Table ndash 104 Size and Position of Openings in Bearing Walls
S
No
Position of opening Details of Opening for Building Category
A and B C D and E
1 Distance b5 from the inside corner of outside wall Min Zero mm 230 mm 450 mm
2 For total length of openings the ratio (b1+b2+b3)l1 or
(b6+b7)l2 shall not exceed
a) one-storeyed building
b) two-storeyed building
c) 3 or 4-storeyed building
060
050
042
055
046
037
050
042
033
3 Pier width between consecutive openings b4 Min 340 mm 450 mm 560 mm
4 Vertical distance between two openings one above the
other h3 Min
600 mm 600 mm 600 mm
5 Width of opening of ventilator b8 Max 900 mm 900 mm 900 mm
Openings in any storey shall preferably have their top at the same level so that a continuous
band could be provided over them including the lintels throughout the building
Where openings do not comply with the guidelines as given in Table ndash 104 they should be
strengthened by providing reinforced concrete or reinforcing the brickwork as shown in Fig
1017 with high strength deformed (HSD) bars of 8 mm dia but the quantity of steel shall be
increased at the jambs
If a window or ventilator is to be
projected out the projection shall be in
reinforced masonry or concrete and well
anchored
If an opening is tall from bottom to
almost top of a storey thus dividing the
wall into two portions these portions
shall be reinforced with horizontal
reinforcement of 6 mm diameter bars at
not more than 450 mm intervals one on
inner and one on outer face properly tied
to vertical steel at jambs corners or
junction of walls where used
The use of arches to span over the
openings is a source of weakness and
shall be avoided Otherwise steel ties
should be provided
109 भको पी सदढ़ीकरण वयवसथा Seismic Strengthening Arrangements
All masonry buildings shall be strengthened as specified for various categories of buildings as
listed in Table ndash 105
Fig 1017 Strengthening Masonry around Opening (IS
4326 1993)
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Table ndash 105 Strengthening Arrangements Recommended for Masonry Buildings
(Rectangular Masonry Units)(IS 4326 1993)
Building Category Number of Storeyes Strengthening to be Provided in all Storeys
A
i) 1 to 3
ii) 4
a
a b c
B
i) 1 to 3
ii) 4
a b c f g
a b c d f g
C
i) 1 and 2
ii) 3 and 4
a b c f g
a to g
D
i) 1 and 2
ii) 3 and 4
a to g
a to h
E 1 to 3 a to h
Where
a mdash Masonry mortar
b mdash Lintel band
c mdash Roof band and gable band where necessary
d mdash Vertical steel at corners and junctions of walls
e mdash Vertical steel at jambs of openings
f mdash Bracing in plan at tie level of roofs
g mdash Plinth band where necessary and
h mdash Dowel bars
4th storey not allowed in category E
NOTE mdash In case of four storey buildings of category B the requirements of vertical steel may be checked
through a seismic analysis using a design seismic coefficient equal to four times the one given in (a) 3423
of IS 1893 1984 (This is because the brittle behaviour of masonry in the absence of vertical steel results in
much higher effective seismic force than that envisaged in the seismic coefficient provided in the code) If
this analysis shows that vertical steel is not required the designer may take the decision accordingly
The overall strengthening arrangements to be adopted for category D and E buildings which
consist of horizontal bands of reinforcement at critical levels vertical reinforcing bars at corners
junctions of walls and jambs of opening are shown in Fig 1018 amp 1019
Fig 1018 Overall Arrangement of Reinforcing Fig 1019 Overall Arrangement of Reinforcing Masonry
Masonry Buildings (IS 4326 1993) Building having Pitched Roof (IS 4326 1993)
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1091 पटट का अनभाग एवो सदढीकरण Section and Reinforcement of Band
The band shall be made of reinforced concrete of grade not leaner than M15 or reinforced
brickwork in cement mortar not leaner than 13 The bands shall be of the full width of the wall
not less than 75 mm in depth and reinforced with steel as indicated in Table ndash 106
Table ndash 106 Recommended Longitudinal Steel in Reinforced Concrete Bands (IS 4326 1993)
Span Building Category
B
Building Category
C
Building Category
D
Building Category
E No of Bars Dia No of Bars Dia No of Bars Dia No of Bars Dia
(1) (2) (3) (4) (5) (6) (7) (8) (9)
m mm mm mm mm
5 or less 2 8 2 8 2 8 2 10
6 2 8 2 8 2 10 2 12
7 2 8 2 10 2 12 4 10
8 2 10 2 12 4 10 4 12
Notes -
1 Span of wall will be the distance between centre lines of its cross walls or buttresses For spans greater than 8 m
it will be desirable to insert pillasters or buttresses to reduce the span or special calculations shall be made to
determine the strength of wall and section of band
2 The number and diameter of bars given above pertain to high strength deformed bars If plain mild-steel bars are
used keeping the same number the following diameters may be used
High Strength Def Bar dia 8 10 12 16 20
Mild Steel Plain bar dia 10 12 16 20 25
3 Width of RC band is assumed same as the thickness of the wall Wall thickness shall be 200 mm minimum A
clear cover of 20 mm from face of wall will be maintained
4 The vertical thickness of RC band be kept 75 mm minimum where two longitudinal bars are specified one on
each face and 150 mm where four bars are specified
5 Concrete mix shall be of grade M15 of IS 456 1978 or 1 2 4 by volume
6 The longitudinal steel bars shall be held in position by steel links or stirrups 6 mm dia spaced at 150 mm apart
NOTE mdash In coastal areas the concrete grade shall be M20 concrete and the filling mortar of 13
(cement-sand with water proofing admixture)
As illustrated in Fig 1020 ndash
In case of reinforced brickwork the
thickness of joints containing steel bars shall
be increased so as to have a minimum
mortar cover of 10 mm around the bar In
bands of reinforced brickwork the area of
steel provided should be equal to that
specified above for reinforced concrete
bands
In category D and E buildings to further
iterate the box action of walls steel dowel
bars may be used at corners and T-junctions
of walls at the sill level of windows to
length of 900 mm from the inside corner in
each wall Such dowel may be in the form of
Fig 1020 Reinforcement and Bending Detail in RC Band ((IS 4326 1993)
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U stirrups 8 mm dia Where used such bars must be laid in 13 cement-sand-mortar with a
minimum cover of 10 mm on all sides to minimize corrosion
1010 भको प क दौरान सटोन तचनाई की दीवारो ो का वयविार Behaviour of Stone Masonry
Walls during Earthquakes
Stone has been used in building construction in India since ancient times since it is durable and
locally available The buildings made of thick stone masonry walls (thickness ranges from 600 to
1200 mm) are one of the most deficient building systems from earthquake-resistance point of
view
The main deficiencies include excessive wall thickness absence of any connection between the
two wythes of the wall and use of round stones (instead of shaped ones) (Fig 1021 amp 1022)
Note A wythe is a continuous vertical section of masonry one unit in thickness A wythe may be
independent of or interlocked with the adjoining wythe (s) A single wythe of brick that is not
structural in nature is referred to as a veneer (httpsenwikipediaorgwikiWythe)
The main patterns of earthquake damage include
(a) bulging separation of walls in the horizontal direction into two distinct wythes
(b) separation of walls at corners and T-junctions
(c) separation of poorly constructed roof from walls and eventual collapse of roof and
(d) disintegration of walls and eventual collapse of the whole dwelling
In the 1993 Killari (Maharashtra) earthquake alone over 8000 people died most of them buried
under the rubble of traditional stone masonry dwellings Likewise a majority of the over 13800
deaths during 2001 Bhuj (Gujarat) earthquake is attributed to the collapse of this type of
construction
1011 भको प परतिरोधी सटोन तचनाई भवन क तनमायण िि सामानय तसदाोि General principle for
construction of Earthquake Resistant stone masonry building
10111 भको प परतिरोधी लकषण Earthquake Resistant Features
1 Low strength stone masonry buildings are weak against earthquakes and should be avoided
in high seismic zones Inclusion of special earthquake-resistant features may enhance the
earthquake resistance of these buildings and reduce the loss of life These features include
Fig 1021 Separation of a thick wall into two layers Fig 1022 Separation of unconnected adjacent walls at junction
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(a) Ensure proper wall construction
(b) Ensure proper bond in masonry courses
(c) Provide horizontal reinforcing elements
(d) Control on overall dimensions and heights
2 The mortar should be cement-sand (1 6) lime-sand (1 3) or clay mud of good quality
3 The wall thickness should not be larger than 450
mm Preferably it should be about 350 mm and
the stones on the inner and outer wythes should be
interlocked with each other
NOTE - If the two wythes are not interlocked they
tend to delaminate during ground shaking bulge
apart (as shown in Fig 1023) and buckle
separately under vertical load leading to
complete collapse of the wall and the building
4 The masonry should preferably be brought to courses at not more than 600 mm lift
5 lsquoThroughrsquo stones at full length
equal to wall thickness should be
used in every 600 mm lift at not
more than 12 m apart
horizontally If full length stones
are not available stones in pairs
each of about 34 of the wall
thickness may be used in place of
one full length stone so as to
provide an overlap between them
(as shown in Fig 1024)
6 In place of lsquothroughrsquo stones lsquobonding elementsrsquo of steel bars 8 to 10 mm dia bent to S-shape
or as hooked links may be used with a cover of 25 mm from each face of the wall (as shown
in Fig 1024) Alternatively wood-bars of 38 mm X 38 mm cross section or concrete bars of
50 mm X50 mm section with an 8 mm dia rod placed centrally may be used in place of
throughrsquo stones The wood should be well treated with preservative so that it is durable
against weathering and insect action
7 Use of lsquobondingrsquo elements of adequate length should also be made at corners and junctions of
walls to break the vertical joints and provide bonding between perpendicular walls
8 Height of the stone masonry walls (random rubble or half-dressed) should be restricted as
follows with storey height to be kept 30 m maximum and span of walls between cross walls
to be limited to 50 m
Fig 1023 Wall delaminated with buckled
withes (IS 13828 1993)
Fig 1024 Through Stone and Bond Elements (IS 13828 1993)
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a) For categories A and B ndash Two storeys with flat roof or one storey plus attic if walls are
built in lime-sand or mud mortar and -one storey higher if walls are built in cement-sand
1 6 mortar
b) For categories C and D - Two storeys with flat roof or two storeys plus attic for pitched
roof if walls are built in 1 6 cement mortar and one storey with flat roof or one storey
plus attic if walls are built in lime-sand or mud mortar respectively
9 If walls longer than 5 m are needed buttresses may be used at intermediate points not farther
apart than 40 m The size of the buttress be kept of uniform thickness Top width should be
equal to the thickness of main wall t and the base width equal to one sixth of wall height
10 The stone masonry dwellings must have horizontal bands (plinth lintel roof and gable
bands) These bands can be constructed out of wood or reinforced concrete and chosen based
on economy It is important to provide at least one band (either lintel band or roof band) in
stone masonry construction
Note Although this type of stone masonry construction practice is deficient with regards to earthquake
resistance its extensive use is likely to continue due to tradition and low cost But to protect human lives
and property in future earthquakes it is necessary to follow proper stone masonry construction in seismic
zones III and higher Also the use of seismic bands is highly recommended
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अधयाय Chapter- 11
भकपीय रलयमकन और रटरोफिट ग
SEISMIC EVALUATION AND RETROFITTING
There are considerable number of buildings that do not meet the requirements of current design
standards because of inadequate design or construction errors and need structural upgrading
specially to meet the seismic requirements
Retrofitting is the best solution to strengthen such buildings without replacing them
111 भकपीय रलयमकन SEISMIC EVALUATION
Seismic evaluation is to assess the seismic response of buildings which may be seismically
deficient or earthquake damaged for their future use The evaluation is also helpful in choosing
appropriate retrofitting techniques
The methods available for seismic evaluation of existing buildings can be broadly divided into
two categories
1 Qualitative methods 2 Analytical methods
1111 गणमतरक िरीक QUALITATIVE METHODS
The qualitative methods are based on the available background information of the structures
past performance of similar structures under severe earthquakes visual inspection report some
non-destructive test results etc
Method for Seismic evaluation
Qualitative methods Analytic methods
CapacityDemand
method
Push over
analysis
Inelastic time
history method
Condition
assessment
Visual
inspection
Non-destructive
testing
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The evaluation of any building is a difficult task which requires a wide knowledge about the
structures cause and nature of damage in structures and its components material strength etc
The proposed methodology is divided into three components
1 Condition assessment
It is based on
data collection or information gathering of structures from architectural and structural
drawings
performance characteristics of similar type of buildings in past earthquakes
rapid evaluation of strength drift materials structural components and structural details
2 Visual inspectionField evaluation It is based on observed distress and damage in
structures Visual inspection is more useful for damaged structures however it may also be
conducted for undamaged structures
3 Non-destructive evaluation It is generally carried out for quick estimation of materials
strength determination of the extent of determination and to establish causes remain out of
reach from visual inspection and determination of reinforcement and its location NDT may
also be used for preparation of drawing in case of non-availability
11111 Condition Assessment for Evaluation
The aim of condition assessment of the structure is the collection of information about the
structure and its past performance characteristics to similar type of structure during past
earthquakes and the qualitative evaluation of structure for decision-making purpose More
information can be included if necessary as per requirement
(i) Data collection information gathering
Collection of the data is an important portion for the seismic evaluation of any existing building
The information required for the evaluated building can be divided as follows
Building Data
Architectural structural and construction drawings
Vulnerability parameters number of stories year of construction and total floor area
Specification soil reports and design calculations
Seismicity of the site
Construction Data
Identifications of gravity load resisting system
Identifications of lateral load resisting system
Maintenance addition alteration or modifications in structures
Field surveys of the structurersquos existing condition
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Structural Data
Materials
Structural concept vertical and horizontal irregularities torsional eccentricity pounding
short column and others
Detailing concept ductile detailing special confinement reinforcement
Foundations
Non-structural elements
(ii) Past Performance data
Past performance of similar type of structure during the earthquake provides considerable amount
of information for the building which is under evaluation process Following are the areas of
concerns which are responsible for poor performance of buildings during earthquake
Material concerns
Low grade on concrete
Deterioration in concrete and reinforcement
High cement-sand ratio
Corrosion in reinforcement
Use of recycled steel as reinforcement
Spalling of concrete by the corrosion of embedded reinforcing bars
Corrosion related to insufficient concrete cover
Poor concrete placement and porous concrete
Structural concerns
The relatively low stiffness of the frames excessive inter-storey drifts damage to non-
structural items
Pounding column distress possibly local collapse
Unsymmetrical buildings (U T L V) in plan torsional effects and concentration of damage
at the junctures (ie re-entrant corners)
Unsymmetrical buildings in elevation abrupt change in lateral resistance
Vertical strength discontinuities concentrate damage in the ldquosoftrdquo stories
Short column
Detailing concerns
Large tie spacing in columns lack of confinement of concrete core shear failures
Insufficient column lengths concrete to spall
Locations of inadequate splices brittle shear failure
Insufficient column strength for full moment hinge capacity brittle shear failure
Lack of continuous beam reinforcement hinge formation during load reversals
Inadequate reinforcing of beam column joints or location of beam bar splices at columns
joint failures
Improper bent-up of longitudinal reinforcing in beams as shear reinforcement shear failure
during load reversal
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Foundation dowels that are insufficient to develop the capacity of the column steel above
local column distress
(iii) Seismic Evaluation Data
Seismic evaluation of data will provide a general idea about the building performance during an
earthquake The criteria of evaluation of building will depend on materials strength and ductility
of structural components and detailing of reinforcement
Material Evaluation
Buildings height gt 3 stories minimum grade concrete M 20 desirable M 30 to M 40
particularly in columns of lower stories
Maximum grade of steel should be Fe 415 due to adequate ductility
No significant deterioration in reinforcement
No evidence of corrosion or spalling of concrete
Structural components
Evaluation of columns shear strength and drift check for permissible limits
Evaluation of plan irregularities check for torsional forces and concentration of forces
Evaluation of vertical irregularities check for soft storey mass or geometric discontinuities
Evaluation of beam-column joints check for strong column-weak beams
Evaluation of pounding check for drift control or building separation
Evaluation of interaction between frame and infill check for force distribution in frames and
overstressing of frames
(i) Flexural members
Limitation of sectional dimensions
Limitation on minimum and maximum flexural reinforcement at least two continuous
reinforced bars at top and bottom of the members
Restriction of lap splices
Development length requirements for longitudinal bars
Shear reinforcement requirements stirrup and tie hooks tie spacing bar splices
(ii) Columns
Limitation of sectional dimensions
Longitudinal reinforcement requirement
Transverse reinforcement requirements stirrup and tie hooks column tie spacing
column bar splices
Special confining requirements
(iii) Foundation
Column steel doweled into the foundation
Non-structural components
Cornices parapet and appendages are anchored
Exterior cladding and veneer are well anchored
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11112 Field Evaluation Visual Inspection Method
The procedure for visual inspection method is as below
Equipments
Optical magnification allows a detailed view of local areas of distress
Stereomicroscope that allow a three dimensional view of the surface Investigator can
estimate the elevation difference in surface features by calibrating the focus adjustment
screw
Fibrescope and borescopes allow inspection of regions that are inaccessible to the naked eye
Tape to measure the dimension of structure length of cracks
Flashlight to aid in lighting the area to be inspected particularly in post-earthquake
evaluation power failure
Crack comparator to measure the width of cracks at representative locations two types
plastic cards and magnifying lens comparators
Pencil to draw the sketch of cracks
Sketchpad to prepare a representation of wall elevation indicating the location of cracks
spalling or other damage records of significant features such as non-structural elements
Camera for photographs or video tape of the observed cracking
Action
Perform a walk through visual inspection to become familiar with the structure
Gather background documents and information on the design construction maintenance
and operation of structure
Plan the complete investigation
Perform a detailed visual inspection and observe type of damage cracks spalls and
delaminations permanent lateral displacement and buckling or fracture of reinforcement
estimating of drift
Observe damage documented on sketches interpreted to assess the behaviour during
earthquake
Perform any necessary sampling basis for further testing
Data Collection
To identify the location of vertical structural elements columns and walls
To sketch the elevation with sufficient details dimensions openings observed damage such
as cracks spalling and exposed reinforcing bars width of cracks
To take photographs of cracks use marker paint or chalk to highlight the fine cracks or
location of cracks in photographs
Observation of the non-structural elements inter-storey displacement
Limitations
Applicable for surface damage that can be visualised
No identification of inner damage health monitoring of building chang of frequency and
mode shapes
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11113 Non-destructive testing (NDT)
Visual inspection has the obvious limitation that only visible surface can be inspected Internal
defects go unnoticed and no quantitative information is obtained about the properties of the
concrete For these reasons a visual inspection is usually supplemented by NDT methods Other
detailed testing is then conducted to determine the extent and to establish causes
NDT tests for condition assessment of structures
Some methods of field and laboratory testing that may assess the minimum concrete strength and
condition and location of the reinforcement in order to characterize the strength safety and
integrity are
(i) Rebound hammer Swiss hammer
The rebound hammer is the most widely used non-destructive device for quick surveys to assess
the quality of concrete In 1948 Ernest Schmidt a Swiss engineer developed a device for testing
concrete based upon the rebound principal strength of in-place concrete comparison of concrete
strength in different locations and provides relative difference in strength only
Limitations
Not give a precise value of compressive strength provide estimate strength for comparison
Sensitive to the quality of concrete carbonation increases the rebound number
More reproducible results from formed surface rather than finished surface smooth hard-
towelled surface giving higher values than a rough-textured surface
Surface moisture and roughness also affect the reading a dry surface results in a higher
rebound number
Not take more than one reading at the same spot
(ii) Penetration resistance method ndash Windsor probe test
Penetration resistance methods are used to determine the quality and compressive strength of in-
situ concrete It is based on the determination of the depth of penetration of probes (steel rods or
pins) into concrete by means of power-actuated driver This provides a measure of the hardness
or penetration resistance of the material that can be related to its strength
Limitations
Both probe penetration and rebound hammer test provide means of estimating the relative
quality of concrete not absolute value of strength of concrete
Probe penetration results are more meaningful than the results of rebound hammer
Because of greater penetration in concrete the prove test results are influenced to a lesser
degree by surface moisture texture and carbonation effect
Probe test may be the cause of minor cracking in concrete
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(iii) Rebar locatorconvert meter
It is used to determine quantity location size and condition of reinforcing steel in concrete It is
also used for verifying the drawing and preparing as-built data if no previous information is
available These devices are based on interaction between the reinforcing bars and low frequency
electromagnetic fields Commercial convert meter can be divided into two classes those based
on the principal of magnetic reluctance and those based on eddy currents
Limitations
Difficult to interpret at heavy congestion of reinforcement or when depth of reinforcement is
too great
Embedded metals sometimes affect the reading
Used to detect the reinforcing bars closest to the face
(iv) Ultrasonic pulse velocity
It is used for determination the elastic constants (modulus of elasticity and Poissonrsquos ratio) and
the density By conducting tests at various points on a structure lower quality concrete can be
identified by its lower pulse velocity Pulse-velocity measurements can detect the presence of
voids of discontinuities within a wall however these measurements can not determine the depth
of voids
Limitations
Moisture content an increase in moisture content increases the pulse velocity
Presence of reinforcement oriented parallel to the pulse propagation direction the pulse may
propagate through the bars and result is an apparent pulse velocity that is higher than that
propagating through concrete
Presence of cracks and voids increases the length of the travel path and result in a longer
travel time
(v) Impact echo
Impact echo is a method for detecting discontinuities within the thickness of a wall An impact-
echo test system is composed of three components an impact source a receiving transducer and
a waveform analyzer or a portable computer with a data acquisition
Limitations
Accuracy of results highly dependent on the skill of the engineer and interpreting the results
The size type sensitivity and natural frequency of the transducer ability of FFT analyzer
also affect the results
Mainly used for concrete structures
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(vi) Spectral analysis of surface waves (SASW)
To assess the thickness and elastic stiffness of material size and location of discontinuities
within the wall such as voids large cracks and delimitations
Limitations
Interpretation of results is very complex
Mainly used on slab and other horizontal surface to determine the stiffness profiles of soil
sites and of flexible and rigid pavement systems measuring the changes in elastic properties
of concrete slab
(vii) Penetrating radar
It is used to detect the location of reinforcing bars cracks voids or other material discontinuities
verify thickness of concrete
Limitations
Mainly used for detecting subsurface condition of slab-on-grade
Not useful for detecting the small difference in materials
Not useful for detecting the size of bars closely spaced bars make difficult to detect features
below the layer of reinforcing steel
1112 ववशलषणमतरक िरीक ANALYTICAL METHODS
Analytical methods are based on considering capacity and ductility of the buildings which are
based on detailed dynamic analysis of buildings The methods in this category are
capacitydemand method pushover analysis inelastic time history analysis etc Brief discussions
on the method of evaluation are as follows
11121 CapacityDemand (CD) method
The forces and displacements resulting from an elastic analysis for design earthquake are
called demand
These are compared with the capacity of different members to resist these forces and
displacements
A (CD) ratio less than one indicate member failure and thus needs retrofitting
When the ductility is considered in the section the demand capacity ratio can be equated to
section ductility demand of 2 or 3
The main difficulty encountered in using this method is that there is no relationship between
member and structure ductility factor because of non-linear behaviour
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11122 Push Over Analysis
The push over analysis of a structure is a static non-linear analysis under permanent vertical
loads and gradually increasing lateral loads
The equivalent static lateral loads approximately represent earthquake-induced forces
A plot of total base shear verses top displacement in a structure is obtained by this analysis
that would indicate any premature failure or weakness
The analysis is carried out up to failure thus it enables determination of collapse load and
ductility capacity
On a building frame loaddisplacement is applied incrementally the formation of plastic
hinges stiffness degradation and plastic rotation is monitored and lateral inelastic force
versus displacement response for the complete structure is analytically computed
This type of analysis enables weakness in the structure to be identified The decision to
retrofit can be taken on the basis of such studies
11123 Inelastic time-history analysis
A seismically deficient building will be subjected to inelastic action during design earthquake
motion
The inelastic time history analysis of the building under strong ground motion brings out the
regions of weakness and ductility demand in the structure
This is the most rational method available for assessing building performance
There are computer programs available to perform this type of analysis
However there are complexities with regard to biaxial inelastic response of columns
modelling of joints behaviour interaction of flexural and shear strength and modelling of
degrading characteristics of member
The methodology is used to ascertain deficiency and post-elastic response under strong
ground shaking
Fig ndash 111 Strengthening strategies
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112 भवनो की रटरोफिट ग Retrofitting of Building
Retrofitting is to upgrade the strength and structural capacity of an existing structure to enable it
to safely withstand the effect of strong earthquakes in future
1121 सकटरचरल लवल यम गलोबल रटरोफि िरीक Structural Level or Global Retrofit
Methods
Two approaches are used for structural-level retrofitting
(i) Conventional Methods
(ii) Non-conventional methods
Retrofit procedure
Detailed seismic
evaluation
Retrofit
techniques
Seismic capacity
assessment
Selection of retrofit
scheme
Design of retrofit
scheme and detailing
Re-evaluation of
retrofit structure
Addition of infill walls
Addition of new
external walls
Addition of bracing
systems
Construction of wing
walls
Strengthening of
weak elements
Structural Level or Global Member Level or Local
Seismic Base Isolation
Jacketing of beams
Jacketing of columns
Jacketing of beam-
column joints
Strengthening of
individual footings
Seismic Dampers
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11211 Conventional Methods
Conventional Methods are based on increasing the seismic resistance of existing structure The
main categories of these methods are as follow
a) Addition of infilled walls
b) Addition of new external walls
c) Addition of bracing system
d) Construction of wing walls
e) Strengthening of weak elements
112111 Addition of infilled walls
The construction of infill walls within the frames of the load bearing structures as shown in the
example of Fig ndash 112 aims to drastically increase the strength and the stiffness of the structure
This method can also be applied in order to correct design errors in the structure and more
specifically when a large asymmetric distribution of strength or stiffness in elevation or an
eccentricity of stiffness in plan have been recognised
Fig - 112 Addition of infilled wall and wing walls
Fig - 113 Frames and shear wall
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As shown in Fig ndash 114 there are two alternatives methods of adding infill walls Either the infill
wall is simply placed between two existing columns or it is extended around the columns to form
a jacket The second method is specifically recommended in order to increase the strength in this
region In the situation where the existing columns are very weak a steel cage should be placed
around the columns before constructing new walls and column jackets In all cases the base of
any new wall should always be connected to the existing foundation
112112 Addition of new external walls
In some cases strengthening by adding concrete walls can be performed externally This can
often be carried out for functional reasons as for example in cases when the building must be
kept in operation during the intervention works New cast-in-place concrete walls constructed
outside the building can be designed to resist part or all the total seismic forces induced in the
building The new walls are preferably positioned adjacent to vertical elements (columns or
walls) of the building and are connected to the structure by placing special compression tensile
or shear connectors at every floor level of the building As shown in Figure 115 new walls
usually have a L-shaped cross-section and are constructed to be in contact with the external
corners of the building
Fig ndash 114 Two alternative methods of adding infill walls
Fig ndash 115 Schematic arrangement of connections between the existing building and
a new wall (a) plan (b) section of compression connector and (c) section of tension
connector
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It is important to ensure that connectors behave elastically under seismic design action effects
For this reason when designing the connectors a resistance safety factor equal to 14 is
recommended The use of compression and tensile connectors instead of shear connectors is
strongly recommended as much higher forces can be transferred It is essential that the anchorage
areas for the connectors on the existing
building and on the new walls have
enough strength to guarantee the transfer
of forces between new walls and the
existing structures
A very important issue of the above
method concerns the foundation of new
walls Foundation conditions should be
improved if large axial forces can be
induced in new walls during seismic
excitation In addition the construction
of short cantilever beams protruding from
the wall underneath the adjacent beams
at every floor level of the building as
shown in Fig ndash 116 appears to be a good solution
112113 Addition of bracing systems
The construction of bracing within
the frames of the load bearing
structure aims for a high increase
in the stiffness and a considerable
increase in the strength and
ductility of the structure Bracing
is normally constructed from steel
elements rather than reinforced
concrete as the elastic
deformation of steel aids the
absorption of seismic energy
Bracing systems can be used in a similar way as that for
steel constructions and can be applied easily in single-
storey industrial buildings with a soft storey ground floor
level where no or few brick masonry walls exist between
columns
Various truss configurations have been applied in
practice examples of which are K-shaped diamond
shaped or cross diagonal The latter is the most common
and is often the most effective solution
Fig ndash 116 Construction of cantilever beams to
transfer axial forces to new walls (a) plan (b)
section c-c
Fig ndash 117 Reinforced Concrete Building retrofitted
with steel bracing
Fig ndash 118 Steel bracing soft storey
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Use of steel bracing has a potential advantage over other schemes for the following reasons
Higher strength and stiffness can be proved
Opening for natural light can be
made easily
Amount of work is less since
foundation cost may be minimised
Bracing system adds much less
weight to the existing structure
Most of the retrofitting work can
be performed with prefabricated
elements and disturbance to the
occupants may be minimised
112114 Construction of wing wall
The construction of reinforced
concrete wing walls in continuous
connection with the existing columns
of a structure as shown above in
example of Fig ndash 112 is a very
popular technique
As presented in Fig ndash 1110 there are
two alternative methods of connecting
the wing wall to the existing load
bearing structure
In the first method the wall is connected to the column and the beams at the top and the base
of any floor level Steel dowels or special anchors are used for the connection and the
reinforcement of the new wall is welded to the existing reinforcement
In the second method the new wing wall is extended around the column to form a jacket
Obviously in this case stresses at the interface between the new concrete and the existing
column are considerably lower when compared to the first method
Moreover uncertainties regarding the capacity of the connection between the wall and the
column do not affect the seismic performance of the strengthened element Therefore the second
alternative method is strongly recommended
Fig ndash 1110 Construction of reinforced concrete wing
wall
Fig ndash 119 Steel bracing
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112115 Strengthening weak elements
The selective strengthening of weak elements of the
structure aims to avoid a premature failure of the critical
elements of a building and to increase the ductility of the
structure
Usually this method is applied to vertical elements and
is accompanied by the construction of fibre reinforced
polymer (FRP) jackets or as shown in Fig- 1111 steel
cages around the vertical elements
If a strength increase is also required this method can
include the construction of column jackets of shotcrete
or reinforced concrete
11212 Non-conventional methods
These are based on reduction of seismic demands Seismic demands are the force and
displacement resulting from an elastic analysis for earthquake design Incorporation of energy
absorbing systems to reduce seismic demands are as follows
(i) Seismic Base Isolation
(ii) Seismic Dampers
112121 Seismic Base Isolation
Isolation of
superstructure from the
foundation is known as
base isolation
It is the most powerful
tool for passive
structural vibration
control technique
Types of base isolations
Elastomeric Bearings
This is the most widely used Base Isolator
The elastomer is made of either Natural Rubber or Neoprene
The structure is decoupled from the horizontal components of the earthquake ground motion
Fig ndash 1111 Construction of a steel
cage around a vertical element
Fig ndash 1112 Base isolated structures
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Sliding System
a) Sliding Base Isolation Systems
It is the second basic type of isolators
This works by limiting the base shear across the
isolator interface
b) Spherical Sliding Base Isolators
The structure is supported by bearing pads that
have curved surface and low friction
During an earthquake the building is free to
slide on the bearings
c) Friction Pendulum Bearing
These are specially designed base isolators
which works on the
principle of simple
pendulum
It increases the natural time
period of oscillation by
causing the structure to
Fig ndash 1113 Elastomeric Isolators Fig ndash 1114 Steel Reinforced Elastomeric
Isolators
Fig ndash 1115 Metallic Roller Bearing
Fig ndash 1116 Spherical Sliding Base
Isolators
Fig ndash 1117 Cross-section of Friction Pendulum Bearing
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slide along the concave inner surface through the frictional interface
It also possesses a re-centering capability
Typically bearings measure 10 m (3 feet) in dia 200 mm (8 inches) in height and weight
being 2000 pounds
d) Advantages of base isolation
Isolate building from ground motion
Building can remain serviceable throughout construction
Lesser seismic loads hence lesser damage to the structure
Minimal repair of superstructure
Does not involve major intrusion upon existing superstructure
e) Disadvantages of base isolation
Expensive
Cannot be applied partially to structures unlike other retrofitting
Challenging to implement in an efficient manner
Allowance for building displacements
Inefficient for high rise buildings
Not suitable for buildings rested on soft soil
112122 Seismic Dampers
Seismic dampers are used in place of structural elements like diagonal braces for controlling
seismic damage in structures
It partly absorbs the seismic energy and reduces the motion of buildings
Types
Viscous Dampers Energy is absorbed by silicon-based fluid passing between piston-
cylinder arrangement
Fig -1118 Cross-section of a Viscous Fluid Damper
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Friction Dampers Energy is absorbed
by surfaces with friction between
rubbing against each other
Yielding Dampers Energy is absorbed
by metallic components that yield
1122 सदसकय सकिर यम सकथमनीय ररटरोफमइ िरीक Member Level or Local Retrofit Methods
The member level retrofit or local retrofit approach is to upgrade the strength of the members
which are seismically deficient This approach is more cost effective as compared to the
structural level retrofit
Jacketing
The most common method of enhancing the individual member strength is jacketing It includes
the addition of concrete steel or fibre reinforced polymer (FRP) jackets for use in confining
reinforced concrete columns beams joints and foundation
Types of jacketing
(1) Concrete jacketing (2) Steel jacketing (3) Strap jacketing
Fig ndash 1119 Friction Dampers
Fig ndash 1120 Yielding Dampers
Fig ndash 1121 Type of Jacketing
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11221 Member level Jacketing
(i) Jacketing of Columns
Different methods of column jacketing are as shown in Figures below
Fig ndash 1122 (b) Column with
CFRP (Carbon Fibre
Reinforced Polymer) Wrap
Fig ndash 1122 (c) Column with Steel Fig ndash 1122 (d) Column with
Jacketing Steel Caging
Fig ndash 1122 (a) Reinforced Concrete Jacketing
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Fig ndash 1122 (e) Construction techniques for Fig ndash 1122 (f) Local strengthening of RC
column jacketing Columns
Fig ndash 1122 (g) Details for provision of longitudinal reinforcement
Fig ndash 1122 (h) Different methods of column jacketing
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(ii) Jacketing of Beam
(iii) Jacketing of Beam-Column Joint
Fig ndash 1123 Different ways of beam jacketing
Fig ndash 1124 Continuity of longitudinal steel in jacketed beams
Fig ndash 1125 Steel cage assembled in the joint
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11222 Table showing the details of reinforced concrete jacketing
Properties of jackets match with the concrete of the existing structure
compressive strength greater than that of the existing
structures by 5 Nmm2 (50 kgcm
2) or at least equal to that
of the existing structure
Minimum width of
jacket 10 cm for concrete cast-in-place and 4 cm for shotcrete
If possible four sided jacket should be used
A monolithic behaviour of the composite column should be
assured
Narrow gap should be provided to prevent any possible
increase in flexural capacity
Minimum area of
longitudinal
reinforcement
3Afy where A is the area of contact in cm2 and fy is in
kgcm2
Spacing should not exceed six times of the width of the new
elements (the jacket in the case) up to the limit of 60 cm
Percentage of steel in the jacket with respect to the jacket
area should be limited between 0015 and 004
At least a 12 mm bar should be used at every corner for a
four sided jacket
Minimum area of
transverse
reinforcement
Designed and spaced as per earthquake design practice
Minimum bar diameter used for ties is not less than 10 mm
diameter anchorage
Due to the difficulty of manufacturing 135 degree hooks on
the field ties made up of multiple pieces can be used
Shear stress in the
interface Provide adequate shear transfer mechanism to assured
monolithic behaviour
A relative movement between both concrete interfaces
(between the jacket and the existing element) should be
prevented
Chipping the concrete cover of the original member and
roughening its surface may improve the bond between the
old and the new concrete
For four sided jacket the ties should be used to confine and
for shear reinforcement to the composite element
For 1 2 3 side jackets as shown in Figures special
reinforcement should be provided to enhance a monolithic
behaviour
Connectors Connectors should be anchored in both the concrete such that
it may develop at least 80 of their yielding stress
Distributed uniformly around the interface avoiding
concentration in specific locations
It is better to use reinforced bars (rebar) anchored with epoxy
resins of grouts as shown in Figure (a)
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11223 Practical aspects in choosing appropriate techniques
Certain issues of practical importance that may help to avoid mistakes in choosing the
appropriate technique are as follows
1) The strengthening of columns by using FRPs or steel jackets is unsuitable for flexible
structures where failure would be controlled by deflection In this case the strengthening
should aim to increase the stiffness
2) It is not favourable to use steel cages or confine with FRPs when an increase in the flexural
capacity of vertical elements is required
3) The application of confinement (with FRPs or steel) to circular or rectangular columns would
increase the ductility and the shear strength and would limit the slippage of overlapping bars
when the lap length has been found to be insufficient However a significant contribution
cannot be expected for columns of rectangular cross section with a large aspect ratio or those
with L-shaped cross sections
4) In the case of columns that have heavily rusted reinforcement strengthening with FRP
jackets (or the application of epoxy glue) will protect the reinforcement from further
oxidation However if the corrosion of the reinforcement is at an advanced stage it is
probable that strengthening may not stop the premature failure of the element
5) The construction of FRP jackets around vertical elements will increase the ductility but it
cannot increase the buckling resistance of the longitudinal reinforcement bars Thus if the
stirrups are too thin in an existing element failure will probably result from the premature
bending of the vertical reinforcement In this case local stress concentrations from the
distressed bars will build up between the stirrups and will lead to a local failure of the jacket
Consequently if bending of the vertical reinforcement has been evaluated as the most likely
cause of column failure the preferable choice for strengthening of the element would be to
place a steel cage
6) In areas where the overlapping of reinforcement bars has been found to be inadequate (short
lap lengths) confining the element with FRPs steel cages or steel jackets will improve the
strength and the ductility of the region considerably However even if it improved the
behaviour it is eventually unfeasible to deter the slipping of bars Consequently when the lap
length of bars has been found to be smaller than 30 of code requirements the solution of
welding of bars must be selected Moreover it must be pointed out that confinement cannot
offer anything to longitudinal bars that are not in the corners of the cross section
7) Experimentally the procedure of placing FRP sheets to strengthen weak beam-column joints
has proved to be particularly effective In practice however this technique has been found to
be difficult to apply due to the presence of slabs and transverse beams The same problems
arise when placing steel plates Other techniques such as the construction of reinforced
concrete jackets or the reconstruction of joints with additional interior reinforcement appear
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to be more beneficial In cases where only a light damage to the joints has been found
repairing with an epoxy resin appears to be particularly effective solution
8) The placing of new concrete in contact with an existing element (by shotcreting and
especially by pouring) will require prior aggravation of the old surface to a depth of at least 6
mm This should be performed by sandblasting or by using suitable mechanical equipment
(for example a scabbler and not just simply a hammer and a chisel) This is to remove the
exterior weak skin of the concrete and to expose the aggregate
9) When placing a new concrete jacket around an existing column it is not always possible to
follow code requirements and place
internal rectangular stirrups to enclose
the middle longitudinal bars as shown
in Fig-1126(a) In this case it is
proposed to place two middle bars in
each side of the jacket so that
octagonal stirrups can be easily
placed as demonstrated in
Fig-1126(b)
In the case where columns have a cross section
with a large aspect ratio the middle longitudinal
bars can be connected by drilling holes through
the section in order to place a S-shaped stirrup as
shown in Fig ndash 1127 After placing stirrups the
remaining void can be filled with epoxy resin In
order to ease placement the S-shaped stirrup can
be prefabricated with one hook and after placing
the second hook can be formed by hand
10) If a thin concrete jacket is to be
placed around a vertical element
and the 135 deg hooks at the ends
of the stirrups are impeded by the
old column it would be
acceptable to decrease the hook
anchorage from 10 times the bar
diameter to 5 or 6 times the bar
diameter as shown in
Fig ndash 1128(a) Otherwise the
ends the stirrups should be
welded together or connected
with special contacts (clamps) as
presented in Fig ndash 1128(b) that have now appeared on the market
(a) (b)
Fig ndash 1126 Placement of internal stirrups in
rectangular cross section
Fig ndash 1127 Placement of an internal
stirrup in a rectangular cross section
with a large aspect ratio
(a) (b)
Fig ndash 1128 Reducing hook lengths and welding the
ends of stirrups
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11) When constructing a jacket around a column it is
important to also strengthen the column joint As shown
in Fig ndash 1129 this can be accomplished by where
possible extending the longitudinal reinforcement bars
around the joint In addition as also shown in
Fig ndash 1129 stirrups must be placed in order to confine
the concrete of the jacket around the joint
In the case where the joint has been found to be
particularly weak a steel diagonal collar can be placed
around the joint before placing the reinforcement as
shown in Fig ndash 1130
12) It is preferable that a new concrete jacket is placed
continuously from the foundation to the top of the building
If this is not possible (due to maintaining the functioning of
the building) it is usual to stop the jacket at the top of the
ground floor level In this case there is a need to anchor the
jacketrsquos longitudinal bars to the existing column This can
be achieved by anchoring a steel plate to the base of the
column of the floor level above and then welding the
longitudinal bars to the anchor plate as shown in Fig ndash
1131
13) In the case where there is a need to reconstruct a heavily damaged column after first shoring
up the column all the defective concrete must be removed so that only good concrete
Fig ndash 1129 Strengthening the
column joint
Fig ndash 1130 Placing a steel diagonal collar
around a weak column joint
Fig ndash 1131 Removal of
defective concrete from a
heavily damaged column
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remains as shown in Fig ndash 1132 Any
buckled reinforcement bars must be welded
to the existing bars Finally the column can
be recast by placing a special non-shrink
concrete
14) In order to anchor new reinforcement bars dowels or anchors with the use of epoxy glue the
diameter of holes drilled into the existing concrete should be roughly 4 mm larger than the
diameter of the bar The best way to remove dust from drilled holes would be to spray water
at the back of the hole The best results (higher adhesive forces) are achieved when the walls
of the hole have been roughened slightly with a small wire brush
15) Care is required when shotcreting in the presence of reinforcement There is a danger of an
accumulation of material building up behind the bars This is usually accredited to material
sticking to the face of bars and may be due to either a low velocity a large firing distance or
insufficient pressure from the compressor
16) The placing of steel plates and especially FRP sheets or fabrics requires special preparation of
the concrete surface to which they will be stuck The rounding of corners and the removal of
surface abnormalities constitute minimal conditions for the application of this technique
17) Two constructional issues that concern the connection of new walls to the old frame require
particular attention The first problem is due to the shrinkage of the new concrete and the
appearance of cracks at the top of the new wall immediately below the old beam in the
region where a good contact between surfaces is essential Here the problem of shrinkage
can be usually dealt with by placing concrete of a particular composition where special
admixtures (for example expansive cements) have been used Alternatively the new wall
could be placed to about 20 cm below the existing beam and after more than 7 days (taking
into account temperature and how new concrete shrinks with time) the void can be filled
with an epoxy or polyster mortar In some cases depending on site conditions (ease of access
dry conditions etc) the new wall can be placed to a height of 2 to 5 mm below the beam and
the void filled with resin glue using the technique of resin injection The second problem
concerns the case of walls from ready-mix concrete and the difficulty of placing the higher
part of the wall due to insufficient access For this reason alone the use of shotcrete should
be the preferred option
Fig ndash 1132 Welding longitudinal bars to an
anchor plate
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113 आरसी भवनो क घ को र समरमनय भकपी कषतियम और उनक उपचमर Common
seismic damage in components of RC Buildings and their remedies
Possible damages in component of RC Buildings which are frequently observed after the
earthquakes are as follows
(i) R C Column
The most common modes of failure of column are as follows
Mode -1 Formation of plastic hinge at the base of ground level columns
Mechanism The column when subjected to seismic
motion its concrete begins to disintegrate and the
load carried by the concrete shifts to longitudinal
reinforcement of the column This additional load
causes buckling of longitudinal reinforcement As a
result the column shortens and looses its ability to
carry even the gravity load
Reasons Insufficient confinement length and
improper confinement in plastic hinge region due to
smaller numbers of ties
Remedies This type of damage is sensitive to the cyclic moments generated during the
earthquake and axial load intensity Consideration is to be paid on plastic hinge length or length
of confinement
Mode ndash 2 Diagonal shear cracking in mid span of columns
Mechanism In older reinforced
concrete building frames column
failures were more frequent since
the strength of beams in such
constructions was kept higher than
that of the columns This shear
failure brings forth loss of axial
load carrying capacity of the
column As the axial capacity
diminishes the gravity loads carried by the column are transferred to neighbouring elements
resulting in massive internal redistribution of forces which is also amplified by dynamic effects
causing spectacular collapse of building
Reason Wide spacing of transverse reinforcement
Remedies To improve understanding of shear strength as well as to understand how the gravity
loads will be supported after a column fails in shear
Fig ndash 1133 Formation of plastic hinge at
the base
Fig ndash 1134 Diagonal shear cracking in mid span of
columns
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Mode ndash 3 Shear and splice failure of longitudinal reinforcement
Mechanism Splices of column
longitudinal reinforcement in
older buildings were
commonly designed for
compression only with
relatively light transverse
reinforcement enclosing the
lap
Under earthquake motion the
longitudinal reinforcement may
be subjected to significant tensile stresses which require lap lengths for tension substantially
exceeding those for compression As a result slip occurs along the splice length with spalling of
concrete
Reasons Deficient lap splices length of column longitudinal reinforcement with lightly spaced
transverse reinforcement particularly if the splices just above the floor slab especially the splices
just above the floor slab which is very common in older construction
Remedies Lap splices should be provided only in the center half of the member length and it
should be proportionate to tension splice Spacing of transverse reinforcement as per IS
139291993
Mode ndash 4 Shear failures in captive columns and short columns
Captive column Column whose deforming ability is restricted and only a fraction of its height
can deform laterally It is due to presence of adjoining non-structural elements columns at
slopping ground partially buried basements etc
Fig - 1135 Shear and splice failure of longitudinal
reinforcement
Fig ndash 1136 Restriction to the Lateral
Displacement of a Column Creating a Captive-
Column Effect
Fig ndash 1137 Captive-column effect in a
building on sloping terrain
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A captive column is full storey slender column whose clear height is reduced by its part-height
contact with a relatively stiff non-structural element such as a masonry infill wall which
constraints its lateral deformation over
the height of contract
The captive column effect is caused by
a non-intended modification to the
original structural configuration of the
column that restricts the ability of the
column to deform laterally by partially
confining it with building components
The column is kept ldquocaptiverdquo by these
components and only a fraction of its
height can deform laterally
corresponding to the ldquofreerdquo portion
thus the term captive column Figure
as given below shows this situation
Short column Column is made shorter than neighbouring column by horizontal structural
elements such as beams girder stair way landing slabs use of grade beams and ramps
Fig ndash 1138 Typical captive-column failure Fig ndash 1139 Column damage due to
captive- column effect
Fig ndash 1140 Captive column caused by ventilation
openings in a partially buried basement
Fig ndash 1141 Short column created by
a stairway landing
Fig ndash 1142 Shear failures in captive columns
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For split-level buildings in order to circumvent the short-column effect the architect should
avoid locating a frame at the vertical plane where the transition between levels occurs For
buildings on slopes special care should be exercised to locate the sloping retaining walls in such
a way that no captive-column effects are induced Where stiff non-structural walls are still
employed these walls should be separated from the structure and in no case can they be
interrupted before reaching the full height of the adjoining columns
Mechanism A reduction in the clear height of captive or short columns increases the lateral
stiffness Therefore these columns are subjected to larger shear force during the earthquake since
the storey shear is distributed in proportion to lateral stiffness of the same floor If these columns
reinforced with conventional longitudinal and transverse reinforcement and subjected to
relatively high axial loading fail by splitting of concrete along their diagonals if the axial
loading level is low the most probable mode of failure is by shear sliding along full depth cracks
at the member ends Moreover in the case of captive column is so effective that usually damage
is shifted to the short non-confined upper section of the column
Reasons Large shear stresses when the structure is subjected to lateral forces are not accounted
for in the standard frame design procedure
Remedies The best solution for captive column or short column is to avoid the situation
otherwise use separation gap in between the non-structural elements and vertical structural
element with appropriate measures against out-of-plane stability of the masonry wall
(ii) R C Beams
The shear-flexure mode of failure is most commonly observed during the earthquakes which is
described as below
Mode ndash 5 Shear-flexure failure
Mechanism Two types of plastic hinges may form in the beams of multi-storied framed
construction depending upon the span of
beams In case of short beams or where
gravity load supported by the beam is
low plastic hinges are formed at the
column ends and damage occurs in the
form of opening of a crack at the end of
beam otherwise there is formation of
plastic hinges at and near end region of
beam in the form of diagonal shear
cracking
Reasons Lack of longitudinal compressive reinforcement infrequent transverse reinforcement in
plastic hinge zone bad anchorage of the bottom reinforcement in to the support or dip of the
longitudinal beam reinforcement bottom steel termination at face of column
Fig ndash 1143 Shear-flexure failure
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Remedies Adequate flexural and shear strength must be provided and verification by design
calculation is essential The beams should not be too stiff with respect to adjacent columns so
that the plastic hinging will occur in beam rather than in column To ensure that the plastic hinges
zones in beams have adequate ductility the following considerations must be considered
Lower and upper limits on the amount of longitudinal flexural tension steel
A limit on the ration of the steel on one side of the beam to that of on the other side
Minimum requirements for the spacing and size of stirrups to restrain buckling of the
longitudinal reinforcement
(iii) R C Beam-Column Joints
The most common modes of failure in beam-column joint are as follows
Mode ndash 6 shear failure in beam-column joint
Mechanism The most common
failure observed in exterior joints are
due to either high shear or bond
(anchorage) under severe
earthquakes Plastic hinges are
formed in the beams at the column
faces As a result cracks develop
throughout the overall beam depth
Bond deterioration near the face of
the column causes propagation of
beam reinforcement yielding in the joint and a shortening of the bar length available for force
transfer by bond causing horizontal bar slippage in the joint In the interior joint the beam
reinforcement at both the column faces undergoes different stress conditions (compression and
tension) because of opposite sights of seismic bending moments results in failure of joint core
Reasons Inadequate anchorage of flexural steel in beams lack of transverse reinforcement
Remedies Exterior Joint ndash The provision on anchorage stub for the beam reinforcement
improves the performance of external joints by preventing spalling of concrete cover on the
outside face resulting in loss of flexural strength of the column This increases diagonal strut
action as well as reduces steel congestion as the beam bars can be anchored clear of the column
bars
(iv) R C Slab
Generally slab on beams performed well during earthquakes and are not dangerous but cracks in
slab creates serious aesthetic and functional problems It reduces the available strength stiffness
and energy dissipation capacity of building for future earthquake In flat slab construction
punching shear is the primary cause of failure The common modes of failure are
Fig - 1144 Shear failure in beam-column joint
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Mode ndash 7 Shear cracking in slabs
Mechanism Damage to slab oftenly
occurs due to irregularities such as large
openings at concentration of earthquake
forces close to widely spaced shear
walls at the staircase flight landings
Reasons Existing micro cracks which
widen due to shaking differential
settlement
Remedies
Use secondary reinforcement in the bottom of the slab
Avoid the use of flat slab in high seismic zones provided this is done in conjunction with a
stiff lateral load resisting system
(v) R C Shear Walls
Shear walls generally performed well during the earthquakes Four types of failure modes are
generally observed
Mode ndash 8 Four types of failure modes are generally observed
(i) Diagonal tension-compression failure in the form of cross-shaped shear cracking
(ii) Sliding shear failure cracking at interface of new and old concrete
(iii) Flexure and compression in bottom end region of wall and finally
(iv) Diagonal tension in the form of X shaped cracking in coupling beams
Fig ndash 1145 Shear cracking in slabs
Fig ndash 1146 Diagonal tension-compression Sliding shear Flexure and compression
failure
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Mechanism Shear walls are subjected to shear and flexural deformation depending upon the
slenderness ratio Therefore the damage in shear walls may generally occurs due to inadequate
shear and flexure capacity of wall Slender walls are governed by their flexural strength and
cracking occurs in the form of yielding of main flexure reinforcement in the plastic hinge region
normally at the base of the wall Squat walls are governed by their shear strength and failure
takes place due to diagonal tension or diagonal compression in the form of inclined cracking
Coupling beams between shear walls or piers may also damage due to inadequate shear and
flexure capacity Sometimes damage occurs at the construction joints in the form of slippage and
related drift
Reasons
Flexuralboundary compression failure Inadequate transverse confining reinforcement to the
main flexural reinforcement near the outer edge of wall in boundary elements
Flexurediagonal tension Inadequate horizontal shear reinforcement
Sliding shear Absence of diagonal reinforcement across the potential sliding planes of the
plastic hinge zone
Coupling beams Inadequate stirrup reinforcement and no diagonal reinforcement
Construction joint Improper bonding between two surfaces
Remedies
The concrete shear walls must have boundary elements or columns thicker than walls which
will carry the vertical load after shear failure of wall
A proper connection between wall versus diaphragm as well as wall versus foundation to
complete the load path
Proper bonding at construction joint in the form of shear friction reinforcement
Provision of diagonal steel in the coupling beam
Fig ndash 1147 Diagonal tension in the form of X shaped
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(v) Infill Walls
Infill panels in reinforced concrete frames are the cause of unequal distribution of lateral forces
in the different frames of a building producing vertical and horizontal irregularities etc the
common mode of failure of infill masonry are in plane or shear failure
Mode ndash 9 Shear failure of masonry infill
Mechanism Frame with infill possesses much more lateral stiffness than the bare frame and
hence initially attracts most of the lateral force during an earthquake Being brittle the infill
starts to disintegrate as soon as its strength is reached Infills that were not adequately tied to the
surrounding frames sometimes dislodges by out-of-plane seismic excitations
Reasons Infill causes asymmetry of load application resulting in increased torsional forces and
changes in the distribution of shear forces between lateral load resisting system
Remedies Two strategies are possible either complete separation between infill walls and frame
by providing separation joint so that the two systems do not interact or complete anchoring
between frame and infill to act as an integral unit Horizontal and vertical reinforcement may also
be used to improve the strength stiffness and deformability of masonry infill walls
(vi) Parapets
Un-reinforced concrete parapets with large height-to-thickness ratio and not in proper anchoring
to the roof diaphragm may also constitute a hazard The hazard posed by a parapet increases in
direct proportion to its height above building base which has been generally observed
The common mode of failure of parapet wall is against out-of-plane forces which is described as
follows
Mode ndash 10 Brittle flexure out-of-plane failure
Mechanism Parapet walls are acceleration sensitive in the out-of-plane direction the result is
that they may become disengaged and topple
Fig ndash 1148 Shear failure of masonry infill
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Reasons Not properly braced
Remedies Analysed for acceleration forces and braced and connected with roof diaphragm
114 चचनमई सरचनमओ की रटरोफिट ग Retrofitting of Masonry Structures
(a) Principle of Seismic Safety of Masonry Buildings
Integral box action
Integrity of various components
- Roof to wall
- Wall to wall at corners
- Wall to foundation
Limit on openings
(b) Methods for Retrofitting of Masonry Buildings
Repairing (Improving existing masonry strength)
Stitching of cracks
Grouting with cement or epoxy
Use of CFRP (Carbon Fibre Reinforced Polymer) strips
Fig ndash 1149 Brittle flexure out-of-plane failure
(a) (b)
Fig ndash 1150 (a) Stitching of cracks Fig ndash 1150 (b) Repair of damaged member in
masonry walls
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(c) Retrofitting of Earthquake vulnerable buildings
External binding or jacketing
Shotcreting
Strengthening of wall intersections
Strengthening by cross wall
Strengthening by buttresses
Strengthening of arches
Fig ndash 1151 Integral Box action
(a) (b)
Fig - 1152 (a) Strengthening of Wall Fig - 1152 (b) Strengthening by
intersections cross wall
(a) (b)
Fig ndash 1153 (a) Strengthening by Fig ndash 1153 (b) Strengthening of Arches
Buttresses
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पररलिष Annexure ndash I
भारिीय भको पी सोतििाएा Indian Seismic Codes
Development of building codes in India started rather early Today India has a fairly good range
of seismic codes covering a variety of structures ranging from mud or low strength masonry
houses to modern buildings However the key to ensuring earthquake safety lies in having a
robust mechanism that enforces and implements these design code provisions in actual
constructions
भको पी तिजाइन कोि का मितव Importance of Seismic Design Codes
Ground vibrations during earthquakes cause forces and deformations in structures Structures
need to be designed to withstand such forces and deformations Seismic codes help to improve
the behaviour of structures so that they may withstand the earthquake effects without significant
loss of life and property An earthquake-resistant building has four virtues in it namely
(a) Good Structural Configuration Its size shape and structural system carrying loads are such
that they ensure a direct and smooth flow of inertia forces to the ground
(b) Lateral Strength The maximum lateral (horizontal) force that it can resist is such that the
damage induced in it does not result in collapse
(c) Adequate Stiffness Its lateral load resisting system is such that the earthquake-induced
deformations in it do not damage its contents under low-to moderate shaking
(d) Good Ductility Its capacity to undergo large deformations under severe earthquake shaking
even after yielding is improved by favourable design and detailing strategies
Seismic codes cover all these aspects
भारिीय भको पी सोतििाएा Indian Seismic Codes
Seismic codes are unique to a particular region or country They take into account the local
seismology accepted level of seismic risk building typologies and materials and methods used
in construction The first formal seismic code in India namely IS 1893 was published in 1962
Today the Bureau of Indian Standards (BIS) has the following seismic codes
1 IS 1893 (Part I) 2002 Indian Standard Criteria for Earthquake Resistant Design of
Structures (5 Revision)
2 IS 4326 1993 Indian Standard Code of Practice for Earthquake Resistant Design and
Construction of Buildings (2nd Revision)
3 IS 13827 1993 Indian Standard Guidelines for Improving Earthquake Resistance of
Earthen Buildings
4 IS 13828 1993 Indian Standard Guidelines for Improving Earthquake Resistance of Low
Strength Masonry Buildings
5 IS 13920 1993 Indian Standard Code of Practice for Ductile Detailing of Reinforced
Concrete Structures Subjected to Seismic Forces
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6 IS 13935 1993 Indian Standard Guidelines for Repair and Seismic Strengthening of
Buildings
The regulations in these standards do not ensure that structures suffer no damage during
earthquake of all magnitudes But to the extent possible they ensure that structures are able to
respond to earthquake shakings of moderate intensities without structural damage and of heavy
intensities without total collapse
IS 1893 (Part I) 2002
IS 1893 is the main code that provides the seismic zone map and specifies seismic design force
This force depends on the mass and seismic coefficient of the structure the latter in turn
depends on properties like seismic zone in which structure lies importance of the structure its
stiffness the soil on which it rests and its ductility For example a building in Bhuj will have
225 times the seismic design force of an identical building in Bombay Similarly the seismic
coefficient for a single-storey building may have 25 times that of a 15-storey building
The revised 2002 edition Part 1 of IS1893 contains provisions that are general in nature and
those applicable for buildings The other four parts of IS 1893 will cover
a) Liquid-Retaining Tanks both elevated and ground supported (Part 2)
b) Bridges and Retaining Walls (Part 3)
c) Industrial Structures including Stack Like Structures (Part 4) and
d) Dams and Embankments (Part 5)
These four documents are under preparation In contrast the 1984 edition of IS1893 had
provisions for all the above structures in a single document
Provisions for Bridges
Seismic design of bridges in India is covered in three codes namely IS 1893 (1984) from the
BIS IRC 6 (2000) from the Indian Roads Congress and Bridge Rules (1964) from the Ministry
of Railways All highway bridges are required to comply with IRC 6 and all railway bridges
with Bridge Rules These three codes are conceptually the same even though there are some
differences in their implementation After the 2001 Bhuj earthquake in 2002 the IRC released
interim provisions that make significant improvements to the IRC6 (2000) seismic provisions
IS 4326 1993 (Reaffirmed 2003)
This code covers general principles for earthquake resistant buildings Selection of materials
and special features of design and construction are dealt with for the following types of
buildings timber constructions masonry constructions using rectangular masonry units and
buildings with prefabricated reinforced concrete roofingflooring elements The code
incorporates Amendment No 3 (January 2005)
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IS 13827 1993 and IS 13828 1993
Guidelines in IS 13827 deal with empirical design and construction aspects for improving
earthquake resistance of earthen houses and those in IS 13828 with general principles of
design and special construction features for improving earthquake resistance of buildings of
low-strength masonry This Masonry includes burnt clay brick or stone masonry in weak
mortars like clay-mud These standards are applicable in seismic zones III IV and V
Constructions based on them are termed non-engineered and are not totally free from collapse
under seismic shaking intensities VIII (MMI) and higher Inclusion of features mentioned in
these guidelines may only enhance the seismic resistance and reduce chances of collapse
IS 13920 1993 (Reaffirmed 2003)
In India reinforced concrete structures are designed and detailed as per the Indian Code IS 456
(2002) However structures located in high seismic regions require ductile design and
detailing Provisions for the ductile detailing of monolithic reinforced concrete frame and shear
wall structures are specified in IS 13920 (1993) After the 2001 Bhuj earthquake this code has
been made mandatory for all structures in zones III IV and V Similar provisions for seismic
design and ductile detailing of steel structures are not yet available in the Indian codes
IS 13935 1993
These guidelines cover general principles of seismic strengthening selection of materials and
techniques for repairseismic strengthening of masonry and wooden buildings The code
provides a brief coverage for individual reinforced concrete members in such buildings but
does not cover reinforced concrete frame or shear wall buildings as a whole Some guidelines
are also laid down for non-structural and architectural components of buildings
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पररलिष Annexure ndash II
Checklist Multiple Choice Questions for Points to be kept in mind during
Construction of Earthquake Resistant Building
S No Description Observer Remarks
1 Seismic Zone in which building is located
i) Zone II ndash Least Seismically Prone Region
ii) Zone III ndash
iii) Zone IV ndash
iv) Zone V ndash Most Seismically Prone Region
Choose Zone
2 Environment condition to which building is exposed
a) Mild b) Moderate c) Severe d) Very Severe e) Extreme
Choose Condition
3 Whether the building is located in Flood Zone YesNo
4 Whether the building is located in Land Slide Zone ie building is on
hill slope or Plane Area
YesNo
5 Type of soil at founding level
a) Rock or Hard Soil
b) Medium Soil
c) Soft Soil
Choose type of soil
6 Type of Building
I) Load Bearing Masonry Building
a) Brick Masonry Construction
b) Stone Masonry construction
II) RCC Framed Structure
a) Regular frame
b) Regular Frame with shear wall
c) Irregular Frame
d) Irregular Frame with shear wall
e) Soft Story Building
Choose type of
building
7 No of Story above Ground Level with provision of Future Extension Mention Storey
8 Category of Building considering Seismic Zone and Importance
Factor (As per Table ndash 102)
i) Category B ndash Building in Seismic Zone II with Importance Factor
10
ii) Category E- Building in Seismic Zone II with Importance Factor
10 and 150
Choose category
9 Bricks should not have compressive strength less than 350 MPa YesNo
10 Minimum wall thickness of brick masonry
i) 1 Brick ndash Single Storey Construction
ii) 1 frac12 Brick ndash In bottom storey up to 3 storey construction amp
1 Brick in top storey with brick masonry
Choose appropriate
11 Height of building is restricted to
i) For A B amp C categories ndash G+2 with flat roof G+1 plus anti for
pitched roof when height of each story not exceed 3 m
ii) D category ndash G+1 with flat Roof
- Ground plus attic for pitched roof
Choose appropriate
12 Max Height of Brick masonry Building ndash 15 m (max 4 storey) YesNo
13 Mortar mix shall be as per Table ndash 102 for category A to E Choose Mortar
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14 Height of Stone Masonry wall
i) For Categories AampB ndash
a) When built in Lime-Sand or Mud mortar
ndash Two storey with flat roof or One Storey plus attic
b) When build in cement sand 16 mortar
- One story higher
ii) For Categories CampD ndash
a) When built in cement Sand 16 Mortar
- Two storey with flat roof or One Storey plus attic for pitched
roof
b) When build in lime sand or Mud mortar
- One story with flat roof or One Story plus attic
Choose appropriate
15 Through stone at full length equal to wall thickness in every 600 mm
lift at not more than 120 m apart horizontally has been provided
YesNo
16 Through stone and Bond Element as per Fig 1024 has been provided YesNo
17 Horizontal Bands
a) Plinth Band
b) Lintel Band
c) Roof Bond
d) Gable Bond
For Over Strengthening Arrangement for Category D amp E Building
have been provided
YesNo
18 Bond shall be made up of Reinforced Concrete of Grade not leaner
than M15 or Reinforced brick work in cement mortar not leaner than
13
YesNo
19 Bond shall be of full width of wall not less than 75 mm in depth and
reinforced with steel as shown in Table ndash 106
YesNo
20 Vertical steel at corners amp junction of wall which are up to 340 mm
(1 frac12 brick) thick shall be provided as shown in Table ndash 101
YesNo
21 General principal for planning building are
i) Building should be as light as possible
ii) All parts of building should be tied together to act as one unit
iii) Projecting part should be avoided
iv) Building having plans with shape L T E and Y shall preferably
be separated in to rectangular parts
v) Structure not to be founded on loose soil which will subside or
liquefy during Earthquake resulting in large differential
settlement
vi) Heavy roofing material should be avoided
vii) Large stair hall shall be separated from Rest of the Building by
means of separation or crumple section
viii) All of the above
ix) None of the above
Choose Correct
22 Structural irregularities may be
i) Horizontal Irregularities
ii) Vertical Irregularities
iii) All of the above
iv) None of the above
Choose Correct
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23 Horizontal Irregularities are
i) Asymmetrical plan shape (eg LTUF)
ii) Horizontal resisting elements (diaphragms)
iii) All of the above
iv) None of the above
Choose Correct
24 Horizontal Irregularities result in
i) Torsion
ii) Diaphragm deformation
iii) Stress Concentration
iv) All of the above
v) None of the above
Choose Correct
25 Vertical Irregularities are
i) Sudden change of stiffness over height of building
ii) Sudden change of strength over height of building
iii) Sudden change of geometry over height of building
iv) Sudden change of mass over height of building
v) All of the above
vi) None of the above
Choose Correct
26 Soft story in one
i) Which has lateral stiffness lt 70 of story above
ii) Which has lateral stiffness lt 80 of average lateral stiffness of 3
storeys above
iii)All of the above
vi) None of the above
Choose Correct
27 Extreme soft storey in one
i) Which has lateral stiffness lt 60 of storey above
ii) Which has lateral stiffness lt 70 of average lateral stiffness of 3
storeys above
iii)All of the above
iv)None of the above
Choose Correct
28 Weak Storey is one
i) Which has lateral strength lt 80 of storey above
ii) Which has lateral strength lt 80 of storey above
iii)All of the above
iv)None of the above
Choose Correct
29 Natural Period of Building
It is the time taken by the building to undergo one complete
cycle of oscillation during shaking
True False
30 Fundamental Natural Period of Building
Natural period with smallest Natural Frequency ie with largest
natural period is called Fundamental Natural Period
True False
31
Type of building frame system
i) Ordinary RC Moment Resisting Frame (OMRF)
ii) Special RC Moment Resisting Frame (SMRF)
iii) Ordinary Shear Wall with OMRF
iv) Ordinary Shear Wall with SMRF
v) Ductile Shear wall with OMRF
vi) Ductile Shear wall with SMRF
vii) All of the above
Choose Correct
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32 Zone factor to be considered for
i) Zone II ndash 010
ii) Zone III ndash 016
iii) Zone IV ndash 024
iv) Zone V ndash 036
True False
33 Importance Factor
i) Important building like school hospital railway station 15
ii) All other buildings 10
True False
34 Design of Earthquake effect is termed as
i) Earthquake Proof Design
or
ii) Earthquake Resistant Design
Choose Correct
35 Seismic Analysis is carried out by
i) Dynamic analysis procedure [Clause 78 of IS1893 (Part I) 2002]
ii) Simplified method referred as Lateral Force Procedure [Clause
75 of IS 1893 (Part I) 2002]
True False
36 Dynamic Analysis is performed for following buildings
(a) Regular Building gt 40 m height in Zone IV amp V
gt 90 height in Zone II amp III
(b) Irregular Building
gt 12 m all framed building in Zone IV amp V
gt 40 m all framed building in Zone II and III
True False
37 Base Shear for Lateral Force Procedure is
VB = Ah W =
True False
38 Distribution of Base Shear to different Floor level is
True False
39 Concept of capacity design is to
Ensure that brittle element will remain elastic at all loads prior to
failure of ductile element
True False
40 lsquoStrong Column ndash Weak Beamrsquo Philosophy is
For a building to remain safe during Earthquake shacking columns
should be stronger than beams and foundation should be stronger
than columns
True False
41 Rigid Diaphragm Action is
Geometric distortion of Slab in horizontal plane under influence of
horizontal Earthquake force is negligible This behaviour is known
as Rigid Diaphragm Action
True False
42 Soft storied buildings are
Column on Ground Storey do not have infill walls (of either
masonry or RC)
True False
43 Soft Storey or Open Ground Story is also termed as weak storey True False
44 Short columns in building suffer significant damage during an earth-
quake
True False
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45 Building can be protected from damage due to Earthquake effect by
using
a) Base Isolation Devices
b) Seismic Dampers
True False
46 Idea behind Base Isolation is
To detach building from Ground so that EQ motion are not
transmitted through the building or at least greatly reduced
True False
47 Base Isolation is done through
Flexible Pads connected to building and foundation True False
48 Seismic Dampers are
(i) Special devices to absorb the energy provided by Ground Motion
to the building
(ii) They act like hydraulic shock absorber in cars
True False
49 Commonly used Seismic Dampers are
(i) Viscous Dampers
(ii) Friction Dampers
(iii) Yielding Dampers
True False
50 For Ductility Requirement
(i) Min Grade of Concrete shall be M20 for all buildings having
more than 3 storeys in height
(ii) Steel Reinforcement of Grade Fe 415 or less only shall be used
(iii) Grade Fe 500 amp Fe 550 having elongation more than 145 may
be used
True False
51 For Ductility Requirement Flexure Members shall satisfy the
following requirement
(i) width of member shall not be less than 200 mm
(ii) width to depth ratio gt 03
(iii) depth of member D lt 14th of clear span
(iv) Factored Axial Stress on the member under Earthquake loading
shall not be greater than 01 fck
True False
52 For Ductility Requirement Longitudinal reinforcement in Flexure
Member shall satisfy the following requirements
i) Top and bottom reinforcement consist of at least 2 bars
throughout member length
ii) Tensile Steel Ratio on any face at any section shall not be less
than ρmin = (024 radic fck) fy
iii) Max Steel ratio on any face at any section shall not exceed
ρmax = 0025
iv) + ve steel at Joint face must be at least equal to half the ndashve steel
at that face
v) Steel provided at each of the top amp bottom face of the member
at any section along its length shall be at least equal to 14th of
max ndashve moment steel provided at the face of either joint
True False
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(vi) Detailing of Reinforcement at Beam-Column Joint
(vii) Detailing of Splicing
53 For Ductile Requirement in compression member
i) Minimum diversion of member shall not be less than 200 mm
ii) In Frames with beams cc Span gt 5m or
unsupported length of column gt 4 m shortest dimension shall not
be less than 300 mm
iii) Ratio of shortest cross sectional dimension to the perpendicular
dimension shall probably not less than 04
True False
54 For Ductile Requirement Longitudinal reinforcement in compression
member shall satisfy the following requirements
i) Lap splice shall be provided only in the central half of the member
length proportional as tension splice
ii) Hoop shall be provided over entire splice length at spacing not
greater than 150 mm
iii) Not more than 50 bar shall be spliced at one section
True False
55 When a column terminates into a footing or mat special confining
reinforcement shall extend at least 300 mm into the footing or mat
True False
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सोदभयगरोथ सची BIBLIOGRAPHY
1 Guidelines for Earthquake Resistant Non-Engineered Construction reprinted by
Indian Institute of Technology Kanpur 208016 India (Source wwwniceeorg)
2 IS 1893 (Part 1) 2002 Criteria for Earthquake Resistant Design Of Structures
PART- 1 GENERAL PROVISIONS AND BUILDINGS (Fifth Revision )
3
IS 4326 1993 (Reaffirmed 1998) Edition 32 (2002-04) Earthquake Resistant
Design and Construction of Buildings ndash Code of Practice ( Second Revision )
(Incorporating Amendment Nos 1 amp 2)
4 IS 13828 1993 (Reaffirmed 1998) Improving Earthquake Resistance of Low
Strength Masonry Buildings ndash Guidelines
5
IS 13920 1993 (Reaffirmed 1998) Edition 12 (2002-03) Ductile Detailing of
Reinforced Concrete Structures subjected to Seismic Forces ndash Code of Practice
(Incorporating Amendment Nos 1 amp 2)
6 IS 13935 1993 (Reaffirmed 1998) Edition 11 (2002-04) Repair and Seismic
Strengthening of Buildings ndash Guidelines (Incorporating Amendment No 1)
7
Earthquake Tips authored by Prof C V R Murty IIT Kanpur and sponsored by
Building Materials and Technology Promotion Council New Delhi India
(Source www wwwiitkacin)
8
Earthquake Engineering Practice Volume 1 Issue 1 March 2007 published by
National Information Center of Earthquake Engineering IIT Kanpur Kanpur
208016
9 Earthquake Resistant Design of Structures by Pankaj Agarwal and Manish
Shrikhande published by PHI Learning Private Limited Delhi 110092 (2015)
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तटपपणी NOTES
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तटपपणी NOTES
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हमारा उददशय
अनरकषि परौधौधगकी और कायापरिाली को उननयन करना तथा उतपादकता और
रलव की पररसमपवियो एव िनशजतत क ननषपादन म सधार करना जिसस
अतववाियो म ववशवसनीयता उपयोधगता और दकषता परापत की िा सकA
Our Objective
To upgrade Maintenance Technologies and Methodologies and achieve
improvement in productivity and performance of all Railway assets and
manpower which inter-alia would cover Reliability Availability and
Utilisation
तिसलमर Disclaimer
The document prepared by CAMTECH is meant for the dissemination of the knowledge information
mentioned herein to the field staff of Indian Railways The contents of this handbookbooklet are only for
guidance Most of the data amp information contained herein in the form of numerical values are indicative
and based on codes and teststrials conducted by various agencies generally believed to be reliable While
reasonable care and effort has been taken to ensure that information given is at the time believed to be fare
and correct and opinion based thereupon are reasonable Due to very nature of research it can not be
represented that it is accurate or complete and it should not be relied upon as such The readeruser is
supposed to refer the relevant codes manuals available on the subject before actual implementation in the
field
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Hkkjrh jsy jkrdquoV ordf dh thou js[kk ---hellip
INDIAN RAILWAYS Lifeline to the nation hellip
If you have any suggestion amp comments please write to us
Contact person Joint Director (Civil)
Phone (0751) - 2470869
Fax (0751) ndash 2470841
Email dircivilcamtechgmailcom
Charbagh Railway Station Lucknow
F o r e w o r d
It is indeed very heartening to know that CAMTECH under the direction from RDSO has brought out a Handbook on ldquoConstruction of Earthquake Resistant Buildingsrdquo
It is also worth mentioning that on IR there were no comprehensive Guidelines or instructions regarding construction of Earthquake Resistant Buildings This handbook shall bridge the gap amp provide technical information on Earthquake phenomenon assessment of magnitude of earthquake general principles for earthquake resistance in Building-layout dynamic response of Buildings
Codal based procedure for determining lateral earthquake forces with special
reference to lsquoDuctility amp Capacity Design Conceptsrsquo has been brought out Solved examples illustrate calculation of design forces for structural members of multi-storied building Provisions contained in Seismic Code IS 1893 amp others have been brought out related to buildings which shall help structural designers and project engineers Chapter on Seismic Evaluation and Retrofitting gives in-sight to serving Engineers in the field to assess building for earthquake resistance and action required thereof in economical manner Thanks are due to Dr SK Thakkar Professor (Retd) IITRoorkee for technical review of this Handbook I congratulate Works amp Bridge Dte of RDSO for editing and Sh DK Gupta Jt Director Civil of CAMTECH involved in compilation of this Handbook for their praise worthy efforts
(J S Sondhi) Addl Director General
RDSO Dt 20072017
पराककथन
दनिया क कई निससो म िाल िी म आए भको पसो ि इमारतसो और जीवि कस काफी िकसाि पहोचाया ि भको प की दनि स दखा जाए तस सबस खतरिाक भवि निमााण
unreinforced ईोट या concrete बलॉक का िसता ि चार मोनजलसो तक क अनिकाोश घरसो कस परबनलत को करीट सलब क साथ burnt clay ईोट नचिाई स निनमात नकया जा रिा ि इसी तरि कई िए चार या पाोच मोनजला घर जस नक छसट और बड शिरसो म परबनलत को करीट फरम स बिाए गए ि म एक उनचत फरम परणाली की कमी रिती ि
िाल िी म आए भको पसो क कारण भारत म इमारतसो और घरसो कस कस सरनित रखा जाय इस पर परमखता स चचाा हई ि भको पीय दशसो म इोजीनियसा कस यि मितवपणा नजममदारी सनिनित करिा ि नक िए निमााण भको प परनतरसिी िसो और यि भी नक उनह मौजदा कमजसर सोरचिाओो दवारा उतपनन समसया का समािाि भी निकालिा ि
यि आशा की जाती ि नक कमटक दवारा तयार पसतिका नसनवल सोरचिाओो क निमााण एवो रखरखाव की गनतनवनियसो म लग भारतीय रलव क इोजीनियररोग कनमायसो क नलए काफी मददगार िसगी
कमटक गवातलयर (ए आर िप) 23 मई 2017 काययकारी तनदशक
FOREWORD
The recent earthquakes occurred in many parts of world has caused considerable damage
to the buildings and lives The most dangerous building construction from an
earthquake point of view is unreinforced brick or concrete block Most houses of upto
four storeys are built of burnt clay brick masonry with reinforced concrete slabs
Similarly many new four or five storey reinforced concrete frame building being
constructed in small and large towns lack a proper frame system
With the recent earthquakes the discussion on how safe buildings and houses are in
India has gained prominence Engineers in seismic countries have the important
responsibility to ensure that the new construction is earthquake resistant and also they
must solve the problem posed by existing weak structures
It is expected that the handbook prepared by CAMTECH will be quite helpful to the
engineering personnel of Indian Railways engaged in construction and maintenance
activities of civil structures
CAMTECHGwalior (AR Tupe)
23 May 2017 Executive Director
भतमका
भारतीय रलव एक बड़ा सगठन ह जिसक पास ससववल इिीननयररग सरचनाओ एव भवनो की ववशाल सपदा मौिद ह भकप की ववनाशकारी परकनत को धयान म रखत हए यह आवशयक ह कक लगभग सभी भवनो चाह व आवासीय ससथागत शकषणिक इतयादद क हो उनकी योिना डििाइन ननमााि तथा रखरखाव भकप परनतरोधी तरीको को अपनाकर ककया िाना चादहए जिसस कक भकप क कारि मानव िीवन व सपवि क नकसान को नयनतम ककया िा सक
ldquoभकप परतिरोधी भवनो क तनरमाणrdquo पर यह हसतपजसतका एक िगह पर पयाापत सामगरी परदान करन का एक परयास ह ताकक वयजतत भवनो क भकप परनतरोधी ननमााि क सलए मलभत ससदधातो को ववकससत कर सही तथा वयवहाररक कायाववधध को अमल म ला सक
इस हसतपजसतका की सामगरी को गयारह अधयायो म ववभाजित ककया गया ह अधयमय-1 पररचय तथा अधयमय-2 भकप इिीननयररग म परयतत शबदावली पररभावित करता ह अधयमय-3 भकप व भकपी खतरो क बार म बननयादी जञान को सकषप म वणिात करता ह अधयमय- 4 भकप पररमाि तथा तीवरता क माप क साथ भारत क भकपीय ज़ोन मानधचतर भकप की ननगरानी क सलए एिससयो क बार म िानकारी परदान करता ह अधयमय-5 व 6 भवन लआउट म भकप परनतरोध क सधार क सलए वयापक ससदधात को बताता ह अधयमय-7 भवन की गनतशील परनतकिया को दशााता ह अधयमय-8 और 9 म कोि पर आधाररत पाशवा बल ननधाारि का तरीका तथा बहमजिला भवन की ldquoितटाइल डिटसलग तथा कपससटी डििाइनrdquo को धयान म रखत हए डििाइन का उदाहरि परसतत ककया गया ह अधयमय-10 म कम शजतत की धचनाई दवारा सरचनाओ क ननमााि को भकप परनतरोधी ससदधातो को धयान म रख वणिात ककया गया ह अधयमय -11 म मौिदा भवनो की भकप परनतरोधी आवशयकताओ को परा करन क सलए भवनो क मौिदा भकपरोधी मलयाकन और पनः सयोिन पर परकाश िाला गया ह
यह हसतपजसतका मखयतः भारतीय रल क फीलि तथा डििाइन कायाालय म कायारत िईएसएसई सतर क सलए ह इस हसतपजसतका को भारतीय रल क ससववल इिीननयसा तथा अनय ववभागो क इिीननयसा दवारा एक सदभा पजसतका क रप म भी इसतमाल ककया िा सकता ह
म शरी एस क ठतकर परोफसर (ररटायिा) आई आई टी रड़की को उनक दवारा ददय गए मागादशान तथा सझावो क सलए अतयनत आभारी ह तथा शरी क सी शातय एसएसईससववल को इस हसतपजसतका क सकलन म उनक समवपात सहयोग क सलए धनयवाद दता ह
यदयवप इस हसतपजसतका को तयार करन म हर तरह की सावधानी बरती गई ह कफर भी कोई तरदट या चक हो तो कपया IRCAMTECHGwalior की िानकारी म लायी िा सकती ह
भारतीय रल क सभी अधधकाररयो और इकाइयो दवारा पसतक की सामगरी म ववसतार तथा सधार क सलए ददय िान वाल सझावो का सवागत ह
कमटक गवातलयर (िी क गपता) 23 मई 2017 सोयकत तनदशकतसतवल
PREFACE
Indian Railways is a big organisation having large assets of Civil Engineering Structures
and Buildings Keeping in mind the destructive nature of Earthquake it is essential that
almost all buildings whether residential institutional educational assembly etc should
be planned designed constructed as well as maintained by adopting Earthquake
Resistant features so that loss due to earthquake to human lives and properties can be
minimised
This handbook on ldquoConstruction of Earthquake Resistant Buildingsrdquo is an attempt to
provide enough material at one place for individual to develop the basic concept for
correctly interpreting and using practices for earthquake resistant construction of
Buildings
Content of this handbook is divided into Eleven Chapters Chapter-1 is Introduction
and Chapter-2 defines Terminology frequently used in Earthquake Engineering
Chapter-3 describes in brief Basic knowledge about Earthquake amp Seismic Hazards
Chapter-4 deals with Measurement of Earthquake magnitude amp intensity with
information about Seismic Zoning Map of India and Agencies for Earthquake
monitoring Chapter-5 amp 6 elaborates General Principle for improving Earthquake
resistance in building layouts Chapter-7 features Dynamic Response of Building In
Chapter-8 amp 9 Codal based procedure for determining lateral loads and Design of
multi-storeyed building with solved example considering Ductile Detailing and Capacity
Design Concept is covered Chapter-10 describes Construction of Low strength
Masonry Structure considering earthquake resistant aspect Chapter-11 enlighten
ldquoSeismic Evaluation amp Retrofittingrdquo for structural upgrading of existing buildings to
meet the seismic requirements
This handbook is primarily written for JESSE level over Indian Railways working in
Field and Design office This handbook can also be used as a reference book by Civil
Engineers and Engineers of other departments of Indian Railways
I sincerely acknowledge the valuable guidance amp suggestion by Shri SK Thakkar
Professor (Retd) IIT Roorkee and also thankful to Shri KC Shakya SSECivil for his
dedicated cooperation in compilation of this handbook
Though every care has been taken in preparing this handbook any error or omission
may please be brought out to the notice of IRCAMTECHGwalior
Suggestion for addition and improvement in the contents from all officers amp units of
Indian Railways are most welcome
CAMTECHGwalior (DK Gupta)
23 May 2017 Joint DirectorCivil
तवषय-सची CONTENT
अधयाय CHAPTER
तववरण DESCRIPTION
पषठ
सोPAGE
NO
पराककथन FOREWORD FROM MEMBER ENGINEERING RLY BOARD पराककथन FOREWORD FROM ADG RDSO पराककथन FOREWORD FROM ED CAMTECH भतमका PREFACE
तवषय-सची CONTENT
सोशोधन पतचययाो CORRECTION SLIPS
1 पररचय Introduction 01
2 भको प इोजीतनयररोग क तलए शबदावली Terminology for Earthquake
Engineering 02-05
3 भको प क बार म About Earthquake 06-16
31 भको प Earthquake 06
32 नकि कारणसो स िसता ि भको प What causes Earthquake 06
33 नववतानिक गनतनवनि Tectonic Activity 06
34 नववतानिक पलट का नसदाोत Theory of Plate Tectonics 07
35 लचीला ररबाउोड नसदाोत Elastic Rebound Theory 11
36 भको प और दसष क परकार Types of Earthquakes and Faults 11
37 जमीि कस निलती ि How the Ground shakes 12
38 भको प या भको पी खतरसो का परभाव Effects of Earthquake or Seismic
Hazards 13
4 भको पी जोन और भको प का मापन Seismic Zone and Measurement
of Earthquake 17-28
41 भको पी जसि Seismic Zone 17
42 भको प का मापि Measurement of Earthquake 19
43 भको प पररमाण सकल क परकार Types of Earthquake Magnitude
Scales 20
44 भको प तीवरता Earthquake Intensity 22
45 भको प निगरािी और सवाओो क नलए एजनसयसो Agencies for Earthquake
Monitoring and Services 28
5 भवन म भको प परतिरोध म सधार क तलए सामानय तसदाोि General
Principle for improving Earthquake Resistance in Building 29-33
51 िलकापि Lightness 29
52 निमााण की निरोतरता Continuity of Construction 29
53 परसजसतटोग एवो ससपडड पाटटास Projecting and Suspended Parts 29
54 भवि की आकनत Shape of Building 29
55 सनविा जिक नबसतडोग लआउट Preferred Building Layouts 30
56 नवनभनन नदशाओो म शसति Strength in Various Directions 30
57 िी ोव Foundations 30
58 छत एवो मोनजल Roofs and Floors 30
59 सीनियाो Staircases 31
510 बॉकस परकार निमााण Box Type Construction 33
511 अनि सरिा Fire Safety 33
6
भको प क दौरान आर सी भवनो ो क परदशयन पर सटरकचरल अतनयतमििाओो
का परभाव Effect of Structural Irregularities on Performance of
RC Buildings during Earthquakes
34-38
61 सटर कचरल अनियनमतताओो का परभाव Effect of Structural Irregularities 34
62 िनतज अनियनमतताएो Horizontal Irregularities 34
63 ऊरधाािर अनियनमतताएो Vertical Irregularities 36
64
भवि नवनयास अनियनमतताएो ndash समसयाए ववशलिि एव ननदान क उपाय Building Irregularities ndash Problems Analysis and Remedial
Measures 37
7 भवन की िायनातमक तवशषिाएा Dynamic Characteristics of
Building 39-47
71 डायिानमक नवशषताए Dynamic Characteristics 39
72 पराकनतक अवनि Natural Period 39
73 पराकनतक आवनि Natural Frequency 39
74 पराकनतक अवनि कस परभानवत करि वाल कारक Factors influencing
Natural Period 40
75 Mode आकनत Mode Shape 42
76 Mode आकनतयसो कस परभानवत करि वाल कारक Factors influencing
Mode Shapes 44
77 सोरचिा की परनतनकरया Response of Structure 46
78 नडजाइि सपटर म Design Spectrum 46
8 तिजाइन पारशय बलो ो क तनधायरण क तलए कोि आधाररि िरीका Code
Based Procedure for Determination of Design Lateral Loads 48-59
81 भको पी नडजाइि की नफलससफ़ी Philosophy of Seismic Design 48
82 भको पी नवशलषण क नलए तरीक Methods for Seismic Analysis 48
83 डायिानमक नवशलषण Dynamic Analysis 49
84 पारशा बल परनकरया Lateral Force Procedure 49
85 को पि की मौनलक पराकनतक अवनि Fundamental Natural Period of
Vibration 52
86 नडजाइि पारशा बल Design Lateral Force 53
87 नडजाइि बल का नवतरण Distribution of Design Force 53
88 नडजाइि उदािरण Design Example ndash To determine Base Shear and
its distribution along Height of Building 54
9 ढााचागि सोरचना का तनमायण Construction of Framed Structure 60-90
91
गरतवाकषाण लसनडोग और भको प लसनडोग म आर सी नबसतडोग का वयविार Behaviour of RC Building in Gravity Loading and Earthquake
Loading 60
92 परबनलत को करीट इमारतसो पर िनतज भको प का परभाव Effect of Horizontal
Earthquake Force on RC Buildings 61
93 िमता नडजाइि सोकलपिा Capacity Design Concept 61
94 लचीलापि और ऊजाा का अपवयय Ductility and Energy Dissipation 62
95 lsquoमजबतिोभ ndash कमजसर बीमrsquo फलससफ़ी lsquoStrong Column ndash Weak
Beamrsquo Philosophy 62
96 कठसर डायाफराम नकरया Rigid Diaphragm Action 63
97
सॉफट सटसरी नबसतडोग क साथ ndash ओपि गराउोड सटसरी नबसतडोग जस नक भको प क
समय कमजसर िसती ि Building with Soft storey ndash Open Ground
Storey Building that is vulnerable in Earthquake 63
98 भको प क दौराि लघ कॉलम वाली इमारतसो का वयविार Behavior of
Buildings with Short Columns during Earthquakes 65
99 भको प परनतरसिी इमारतसो की लचीलापि आवशयकताए Ductility
requirements of Earthquake Resistant Buildings 66
910
बीम नजनह आर सी इमारतसो म भको प बलसो का नवरसि करि क नलए डाला जाता
ि Beams that are required to resist Earthquake Forces in RC
Buildings 66
911 फलकसचरल ममबसा क नलए सामानय आवशयकताए General Requirements
for Flexural Members 68
912
कॉलम नजनह आर सी इमारतसो म भको प बलसो का नवरसि करि क नलए डाला
जाता ि Columns that are required to resist Earthquake Forces in
RC Buildings 69
913 एकसीयल लसडड मबसा क नलए सामानय आवशयकताए General
Requirements for Axial Loaded Members 71
914 बीम-कॉलम जसड जस आर सी भविसो म भको प बलसो का नवरसि करत ि Beam-
Column Joints that resist Earthquakes Forces in RC Buildings 72
915 नवशष सीनमत सदढीकरण Special Confining Reinforcement 74
916
नवशषतः भको पीय ितर म कतरिी दीवारसो वाली इमारतसो का निमााण Construction of Buildings with Shear Walls preferably in Seismic
Regions 75
917 इमपरवड नडजाइि रणिीनतयाो Improved design strategies 76
918 नडजाइि उदािरण Design Example ndash Beam Design of RC Frame
with Ductile Detailing 78
10 अलप सामरथय तचनाई सोरचनाओो क तनमायण Construction of Low
Strength Masonry Structures 91-106
101 भको प क दौराि ईोट नचिाई की दीवारसो का वयविार Behaviour of
Brick Masonry Walls during Earthquakes 91
102 नचिाई वाली इमारतसो म बॉकस एकशि कस सनिनित कर How to ensure
Box Action in Masonry Buildings 92
103 िनतज बड की भनमका Role of Horizontal Bands 93
104 अिसलोब सदढीकरण Vertical Reinforcement 95
105 दीवारसो म सराखसो का सोरिण Protection of Openings in Walls 96
106
भको प परनतरसिी ईोट नचिाई भवि क निमााण ित सामानय नसदाोत General
Principles for Construction of Earthquake Resistant Brick
Masonry Building
97
107 ओपनिोग का परभाव Influence of Openings 100
108 िारक दीवारसो म ओपनिोग परदाि करि की सामानय आवशयकताए General Requirements of Providing Openings in Bearing Walls
100
109 भको पी सदिीकरण वयवसथा Seismic Strengthening Arrangements 101
1010 भको प क दौराि सटसि नचिाई की दीवारसो का वयविार Behaviour of Stone
Masonry Walls during Earthquakes 104
1011
भकप परनतरोधी सटोन धचनाई क ननमााि हत सामानय ससदधात General
Principles for Construction of Earthquake Resistant Stone
Masonry Building
104
11 भकपीय रलयमकन और रटरोफिट ग Seismic Evaluation and
Retrofitting 107-142
111 भकपीय मलयाकन Seismic Evaluation 107
112 भवनो की रटरोकिदटग Retrofitting of Building 116
113
आरसी भवनो क घटको म सामानय भकपी कषनतया और उनक उपचार Common seismic damage in components of RC
Buildings and their remedies 133
114 धचनाई सरचनाओ की रटरोकिदटग Retrofitting of Masonry
Structures 141
Annex ndash I भारिीय भको पी सोतििाएा Indian Seismic Codes 143-145
Annex ndash II Checklist Multiple Choice Questions for Points to be kept in
mind during Construction of Earthquake Resistant Building 146-151
सोदभयगरोथ सची BIBLIOGRAPHY 152
तटपपणी NOTES 153-154
हमारा उददशय एव डिसकलरर OUR OBJECTIVE AND DISCLAIMER
सोशसिि पनचायसो का परकाशि
ISSUE OF CORRECTION SLIPS
इस ििपसतिका क नलए भनवषय म परकानशत िसि वाली सोशसिि पनचायसो कस निमनािसार सोखाोनकत
नकया जाएगा
The correction slips to be issued in future for this handbook will be numbered as
follows
कमटक2017नसईआरबी10सीएस XX नदिाोक_____________________
CAMTECH2017CERB10CS XX date_________________________
जिा xx सोबसतित सोशसिि पची की करम सोखा ि (01 स परारमभ िसकर आग की ओर)
Where ldquoXXrdquo is the serial number of the concerned correction slip (starting
from 01 onwards)
परकातशि सोशोधन पतचययाा W a
CORRECTION SLIPS ISSUED
करसो Sr No
परकाशन
तदनाोक Date of
issue
सोशोतधि पषठ सोखया िथा मद सोखया Page no and Item No modified
तटपपणी Remarks
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अधयाय Chapter ndash 1
पररचय Introduction
To avoid a great earthquake disaster with its severe consequences special consideration must be
given Engineers in seismic countries have the important responsibility to ensure that the new
construction is earthquake resistant and also they must solve the problem posed by existing weak
structures
Most of the loss of life in past earthquakes has occurred due to the collapse of buildings
constructed with traditional materials like stone brick adobe (kachcha house) and wood which
were not particularly engineered to be earthquake resistant In view of the continued use of such
buildings it is essential to introduce earthquake resistance features in their construction
The problem of earthquake engineering can be divided into two parts first to design new
structures to perform satisfactorily during an earthquake and second to retrofit existing structures
so as to reduce the loss of life during an earthquake Every city in the world has a significant
proportion of existing unsafe buildings which will produce a disaster in the event of a strong
ground shaking Engineers have the responsibility to develop appropriate methods of retrofit
which can be applied when the occasion arises
The design of new building to withstand ground shaking is prime responsibility of engineers and
much progress has been made during the past 40 years Many advances have been made such as
the design of ductile reinforced concrete members Methods of base isolation and methods of
increasing the damping in structures are now being utilized for important buildings both new and
existing Improvements in seismic design are continuing to be made such as permitting safe
inelastic deformations in the event of very strong ground shaking
A problem that the engineer must share with the seismologistgeologist is that of prediction of
future occurrence of earthquake which is not possible in current scenario
Earthquake resistant construction requires seismic considerations at all stages from architectural
planning to structural design to actual constructions and quality control
Problems pertaining to Earthquake engineering in a seismic country cannot be solved in a short
time so engineers must be prepared to continue working to improve public safety during
earthquake In time they must control the performance of structures so that effect of earthquake
does not create panic in society and its after effects are easily restorable
To ensure seismic resistant construction earthquake engineering knowledge needs to spread to a
broad spectrum of professional engineers within the country rather than confining it to a few
organizations or individuals as if it were a super-speciality
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अधयाय Chapter ndash 2
भको प इोजीतनयररोग क तलए शबदावली Terminology for Earthquake Engineering
21 फोकस या िाइपोसटर Focus or Hypocenter
In an earthquake the waves emanate from a finite area
of rocks However the point from which the waves
first emanate or where the fault movement starts is
called the earthquake focus or hypocenter
22 इपीसटर Epicentre
The point on the ground surface just above the focus is called the epicentre
23 सििी फोकस भको प Shallow Focus Earthquake
Shallow focus earthquake occurs where the focus is less than 70 km deep from ground surface
24 इोटरमीतिएट फोकस भको प Intermediate Focus Earthquake
Intermediate focus earthquake occurs where the focus is between 70 km to 300 km deep
25 गिरा फोकस भको प Deep Focus Earthquake
Deep focus earthquake occurs where the depth of focus is more than 300 km
26 इपीसटर दरी Epicentre Distance
Distance between epicentre and recording station in km or in degrees is called epicentre distance
27 पवय क झटक Foreshocks
Fore shocks are smaller earthquakes that precede the main earthquake
28 बाद क झटक Aftershocks
Aftershocks are smaller earthquakes that follow the main earthquake
29 पररमाण Magnitude
The magnitude of earthquake is a number which is a measure of energy released in an
earthquake It is defined as logarithm to the base 10 of the maximum trace amplitude expressed
in microns which the standard short-period torsion seismometer (with a period of 08s
Fig 21Basic terminology
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magnification 2800 and damping nearly critical) would register due to the earthquake at an
epicentral distance of 100 km
210 िीवरिा Intensity
The intensity of an earthquake at a place is a measure of the strength of shaking during the
earthquake and is indicated by a number according to the modified Mercalli Scale or MSK
Scale of seismic intensities
211 पररमाण और िीवरिा क बीच बतनयादी फकय Basic difference between Magnitude and
Intensity
Magnitude of an earthquake is a measure of its size
whereas intensity is an indicator of the severity of
shaking generated at a given location Clearly the
severity of shaking is much higher near the
epicenter than farther away
This can be elaborated by considering the analogy
of an electric bulb Here the size of the bulb (100-
Watt) is like the magnitude of an earthquake (M)
and the illumination (measured in lumens) at a
location like the intensity of shaking at that location
(Fig 22)
212 दरवण Liquefaction
Liquefaction is a state in saturated cohesion-less soil wherein the effective shear strength is
reduced to negligible value for all engineering purpose due to pore pressure caused by vibrations
during an earthquake when they approach the total confining pressure In this condition the soil
tends to behave like a fluid mass
213 तववियतनक लकषण Tectonic Feature
The nature of geological formation of the bedrock in the earthrsquos crust revealing regions
characterized by structural features such as dislocation distortion faults folding thrusts
volcanoes with their age of formation which are directly involved in the earth movement or
quake resulting in the above consequences
214 भको पी दरवयमान Seismic Mass
It is the seismic weight divided by acceleration due to gravity
215 भको पी भार Seismic Weight
It is the total dead load plus appropriate amounts of specified imposed load
Fig 22 Reducing illumination with distance
from an electric bulb
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216 आधार Base
It is the level at which inertia forces generated in the structure are transferred to the foundation
which then transfers these forces to the ground
217 दरवयमान का क दर Centre of Mass
The point through which the resultant of the masses of a system acts is called Centre of Mass
This point corresponds to the centre of gravity of masses of system
218 कठोरिा का क दर Centre of Stiffness
The point through which the resultant of the restoring forces of a system acts is called Centre of
stiffness
219 बॉकस परणाली Box System
Box is a bearing wall structure without a space frame where the horizontal forces are resisted by
the walls acting as shear walls
220 पटटा Band
A reinforced concrete reinforced brick or wooden runner provided horizontally in the walls to tie
them together and to impart horizontal bending strength in them
221 लचीलापन Ductility
Ductility of a structure or its members is the capacity to undergo large inelastic deformations
without significant loss of strength or stiffness
222 किरनी दीवार Shear Wall
Shear wall is a wall that is primarily designed to resist lateral forces in its own plane
223 िनय का बयौरा Ductile Detailing
Ductile Detailing is the preferred choice of location and amount of reinforcement in reinforced
concrete structures to provide adequate ductility In steel structures it is the design of members
and their connections to make them adequate ductile
224 लचीला भको पी तवरण गणाोक Elastic Seismic Acceleration Co-Efficient A
This is the horizontal acceleration value as a fraction of acceleration due to gravity versus
natural period of vibration T that shall be used in design of structures
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225 पराकतिक अवतध Natural Period T
Natural period of a structure is its time period of undamped vibration
a) Fundamental Natural Period Tl It is the highest modal time period of vibration along the
considered direction of earthquake motion
b) Modal Natural Period Tk Modal natural period of mode k is the time period of vibration in
mode k
226 नॉमयल मोि Normal Mode
Mode of vibration at which all the masses in a structure attain maximum values of displacements
and rotations and also pass through equilibrium positions simultaneously
227 ओवरसटरगथ Overstrength
Strength considering all factors that may cause its increase eg steel strength being higher than
the specified characteristic strength effect of strain hardening in steel with large strains and
concrete strength being higher than specified characteristic value
228 ररसाोस कमी कारक Response Reduction Factor R
The factor by which the actual lateral force that would be generated if the structure were to
remain elastic during the most severe shaking that is likely at that site shall be reduced to obtain
the design lateral force
229 ररसाोस सकटर म Response Spectrum
The representation of the maximum response of idealized single degree freedom system having
certain period and damping during that earthquake The maximum response is plotted against the
undamped natural period and for various damping values and can be expressed in terms of
maximum absolute acceleration maximum relative velocity or maximum relative displacement
230 तमटटी परोफ़ाइल फकटर Soil Profile Factor S
A factor used to obtain the elastic acceleration spectrum depending on the soil profile below the
foundation of structure
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अधयाय Chapter ndash 3
भको प क बार म About Earthquake
31 भको प Earthquake
Vibrations of earthrsquos surface caused by waves coming from a source of disturbance inside the
earth are described as earthquakes
Earthquake is a natural phenomenon occurring with all uncertainties
During the earthquake ground motions occur in a random fashion both horizontally and
vertically in all directions radiating from epicentre
These cause structures to vibrate and induce inertia forces on them
32 तकन कारणो ो स िोिा ि भको प What causes Earthquake
Earthquakes may be caused by
Tectonic activity
Volcanic activity
Land-slides and rock-falls
Rock bursting in a mine
Nuclear explosions
33 तववियतनक गतितवतध Tectonic Activity
Tectonic activity pertains to geological formation of the bedrock in the earthrsquos crust characterized
by structural features such as dislocation distortion faults folding thrusts volcanoes directly
involved in the earth movement
As engineers we are interested in earthquakes that are large enough and close enough (to the
structure) to cause concern for structural safety- usually caused by tectonic activity
Earth (Fig 31) consists of following segments ndash
solid inner core (radius ~1290km) that consists of heavy
metals (eg nickel and iron)
liquid outer core(thickness ~2200km)
stiffer mantle(thickness ~2900km) that has ability to flow
and
crust(thickness ~5 to 40km) that consists of light
materials (eg basalts and granites)
At the Core the temperature is estimated to be ~2500degC the
pressure ~4 million atmospheres and density ~135 gmcc
this is in contrast to ~25degC 1 atmosphere and 15 gmcc on the surface of the Earth
Fig 31 Inside the Earth
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Due to prevailing high temperature and pressure gradients between the Crust and the Core the
local convective currents in mantle (Fig 32) are developed These convection currents result in a
circulation of the earthrsquos mass hot molten lava comes out and the cold rock mass goes into the
Earth The mass absorbed eventually melts under high temperature and pressure and becomes a
part of the Mantle only to come out again from another location
Near the bottom of the crust horizontal component currents impose shear stresses on bottom of
crust causing movement of plates on earthrsquos surface The movement causes the plates to move
apart in some places and to converge in others
34 तववियतनक पलट का तसदाोि Theory of Plate Tectonics
Tectonic Plates Basic hypothesis of plate tectonics is that the earthrsquos surface consists of a
number of large intact blocks called plates or tectonic plates and these plates move with respect
to each other due to the convective flows of Mantle material which causes the Crust and some
portion of the Mantle to slide on the hot molten outer core The major plates are shown in
Fig 33
The earthrsquos crust is divided into six continental-sized plates (African American Antarctic
Australia-Indian Eurasian and Pacific) and about 14 of sub-continental size (eg Carribean
Cocos Nazca Philippine etc) Smaller platelets or micro-plates also have broken off from the
larger plates in the vicinity of many of the major plate boundaries
Fig 32 Convention current in mantle
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Fig 33 The major tectonic plates mid-oceanic ridges trenches and transform faults of
the earth Arrows indicate the directions of plate movement
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The relative deformation between plates occurs only in narrow zones near their boundaries
These deformations are
1 Aseismic deformation This deformation of the plates occurs slowly and continuously
2 Seismic deformation This deformation occurs with sudden outburst of energy in the form of
earthquakes
The boundaries are (i) Convergent (ii) Divergent (iii) Transform
Convergent boundary Sometimes the plate in the front is slower Then the plate behind it
comes and collides (and mountains are formed) This type of inter-plate interaction is the
convergent boundary (Fig 34)
Divergent boundary Sometimes two plates move away from one another (and rifts are
created) This type of inter-plate interaction is the divergent boundary (Fig 35)
Transform boundary Sometimes two plates move side-by-side along the same direction or in
opposite directions This type of inter-plate interaction is the transform boundary (Fig 36)
Since the deformation occurs predominantly at the boundaries between the plates it would be
expected that the locations of earthquakes would be concentrated near plate boundaries The map
of earthquake epicentres shown in Fig 37 provides strong support to confirm the theory of plate
tectonics The dots represent the epicentres of significant earthquakes It is apparent that the
locations of the great majority of earthquakes correspond to the boundaries between plates
Fig 34 Convergent Boundary
Fig 35 Divergent Boundary
Fig 36 Transform Boundary
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Fig 37 Worldwide seismic activity
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35 लचीला ररबाउोि तसदाोि Elastic Rebound Theory
Earth crust for some reason is moving in opposite
directions on certain faults This sets up elastic
strains in the rocks in the region near this fault As
the motion goes on the stresses build up in the
rocks until the stresses are large enough to cause
slip between the two adjoining portions of rocks
on either side A rupture takes place and the
strained rock rebounds back due to internal stress
Thus the strain energy in the rock is relieved
partly or fully (Fig 38)
Fault The interface between the plates where the movement has taken place is called fault
Slip When the rocky material along the interface of the plates in the Earthrsquos Crust reaches its
strength it fractures and a sudden movement called slip takes place
The sudden slip at the fault causes the earthquake A violent shaking of the Earth during
which large elastic strain energy released spreads out in the form of seismic waves that travel
through the body and along the surface of the
Earth
After elastic rebound there is a readjustment and
reapportion of the remaining strains in the region
The stress grows on a section of fault until slip
occurs again this causes yet another even though
smaller earthquake which is termed as aftershock
The aftershock activity continues until the
stresses are below the threshold level everywhere
in the rock
After the earthquake is over the process of strain build-up at this modified interface between the
tectonic plates starts all over again This is known as the Elastic Rebound Theory (Fig 39)
36 भको प और दोष क परकार Types of Earthquakes and Faults
Inter-plate Earthquakes Most earthquakes occurring along the boundaries of the tectonic
plates are called Inter-plate Earthquakes (eg 1897
Assam (India) earthquake)
Intra-plate Earthquakes Numbers of earthquakes
occurring within the plate itself but away from the
plate boundaries are called Intra-plate Earthquakes
(eg 1993 Latur (India) earthquake)
Note In both types of earthquakes the slip
generated at the fault during earthquakes is along
Fig 310 Type of Faults
Fig 38 Elastic Strain Build-Up and Brittle Rupture
Fig 39 Elastic Rebound Theory
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both vertical and horizontal directions (called Dip Slip) and lateral directions (called Strike
Slip) with one of them dominating sometimes (Fig 310)
37 जमीन कस तिलिी ि How the Ground shakes
Seismic waves Large strain energy released during an earthquake travels as seismic waves in all
directions through the Earthrsquos layers reflecting and refracting at each interface (Fig 311)
There are of two types of waves 1) Body Waves
2) Surface Waves
Body waves are of two types
a) Primary Waves (P-Wave)
b) Secondary Wave (S-Wave)
Surface waves are of two types namely
a) Love Waves
b) Rayleigh Waves
Body Waves Body waves have spherical wave front They consist of
Primary Waves (P-waves) Under P-waves [Fig 311(a)] material particles undergo
extensional and compressional strains along direction of energy transmission These waves
are faster than all other types of waves
Secondary Waves (S-waves) Under S-waves [Fig 311(b)] material particles oscillate at
Fig 311 Arrival of Seismic Waves at a Site
Fig 311(a) Motions caused by Primary Waves
Fig 311(b) Motions caused by Secondary Waves
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right angles to direction of energy transmission This type of wave shears the rock particle to
the direction of wave travel Since the liquid has no shearing resistance these waves cannot
pass through liquids
Surface Waves Surface waves have cylindrical wave front They consist of
Love Waves In case of Love waves [Fig 311(c)] the displacement is transverse with no
vertical or longitudinal components (ie similar to secondary waves with no vertical
component) Particle motion is restricted to near the surface Love waves being transverse
waves these cannot travel in liquids
Rayleigh Waves Rayleigh waves [Fig 311(d)] make a material particle oscillate in an
elliptic path in the vertical plane with horizontal motion along direction of energy
transmission
Note Primary waves are fastest followed in sequence by Secondary Love and Rayleigh waves
38 भको प या भको पी खिरो ो का परभाव Effects of Earthquake or Seismic Hazards
Basic causes of earthquake-induced damage are
Ground shaking
Structural hazards
Liquefaction
Ground failure Landslides
Tsunamis and
Fire
Fig 311(c) Motions caused by Love Waves
Fig 311(d) Motions caused by Rayleigh Waves
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381 जमीन को पन Ground shaking
Ground shaking can be considered to be the most important of all seismic hazards because all
the other hazards are caused by ground shaking
When an earthquake occurs seismic waves radiate away from the source and travel rapidly
through the earthrsquos crust
When these waves reach the ground surface they produce shaking that may last from seconds
to minutes
The strength and duration of shaking at a particular site depends on the size and location of
the earthquake and on the characteristics of the site
At sites near the source of a large earthquake ground shaking can cause tremendous damage
Where ground shaking levels are low the other seismic hazards may be low or nonexistent
Strong ground shaking can produce extensive damage from a variety of seismic hazards
depending upon the characteristics of the soil
The characteristics of the soil can greatly influence the nature of shaking at the ground
surface
Soil deposits tend to act as ldquofiltersrdquo to seismic waves by attenuating motion at certain
frequencies and amplifying it at others
Since soil conditions often vary dramatically over short distances levels of ground shaking
can vary significantly within a small area
One of the most important aspects of geotechnical earthquake engineering practice involves
evaluation of the effects of local soil conditions on strong ground motion
382 सोरचनातमक खिर Structural Hazards
Without doubt the most dramatic and memorable images of earthquake damage are those of
structural collapse which is the leading cause of death and economic loss in many
earthquakes
As the earth vibrates all buildings on the ground surface will respond to that vibration in
varying degrees
Earthquake induced accelerations velocities and displacements can damage or destroy a
building unless it has been designed and constructed or strengthened to be earthquake
resistant
The effect of ground shaking on buildings is a principal area of consideration in the design of
earthquake resistant buildings
Seismic design loads are extremely difficult to determine due to the random nature of
earthquake motions
Structures need not collapse to cause death and damage Falling objects such as brick facings
and parapets on the outside of a structure or heavy pictures and shelves within a structure
have caused casualties in many earthquakes Interior facilities such as piping lighting and
storage systems can also be damaged during earthquakes
However experiences from past strong earthquakes have shown that reasonable and prudent
practices can keep a building safe during an earthquake
Over the years considerable advancement in earthquake-resistant design has moved from an
emphasis on structural strength to emphases on both strength and ductility In current design
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practice the geotechnical earthquake engineer is often consulted for providing the structural
engineer with appropriate design ground motions
383 दरवीकरण Liquefaction
In some cases earthquake damage have occurred when soil deposits have lost their strength and
appeared to flow as fluids This phenomenon is termed as liquefaction In liquefaction the
strength of the soil is reduced often drastically to the point where it is unable to support
structures or remain stable Because it only occurs in saturated soils liquefaction is most
commonly observed near rives bays and other bodies of water
Soil liquefaction can occur in low density saturated sands of relatively uniform size The
phenomenon of liquefaction is particularly important for dams bridges underground pipelines
and buildings standing on such ground
384 जमीन तवफलिा लि सलाइि Ground Failure Land slides
1) Earthquake-induced ground Failure has been observed in the form of ground rupture along
the fault zone landslides settlement and soil liquefaction
2) Ground rupture along a fault zone may be very limited or may extend over hundreds of
kilometers
3) Ground displacement along the fault may be horizontal vertical or both and can be
measured in centimetres or even metres
4) A building directly astride such a rupture will be severely damaged or collapsed
5) Strong earthquakes often cause landslides
6) In a number of unfortunate cases earthquake-induced landslides have buried entire towns
and villages
7) Earthquake-induced landslides cause damage by destroying buildings or disrupting bridges
and other constructed facilities
8) Many earthquake-induced landslides result from liquefaction phenomenon
9) Others landslides simply represent the failures of slopes that were marginally stable under
static conditions
10) Landslide can destroy a building the settlement may only damage the building
385 सनामी Tsunamis
1) Tsunamis or seismic sea waves are generally produced by a sudden movement of the ocean
floor
2) Rapid vertical seafloor movements caused by fault rupture during earthquakes can produce
long-period sea waves ie Tsunamis
3) In the open sea tsunamis travel great distances at high speeds but are difficult to detect ndash
they usually have heights of less than 1 m and wavelengths (the distance between crests) of
several hundred kilometres
4) As a tsunami approaches shore the decreasing water depth causes its speed to decrease and
the height of the wave to increase
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5) As the water waves approach land their velocity decreases and their height increases from
5 to 8 m or even more
6) In some coastal areas the shape of the seafloor may amplify the wave producing a nearly
vertical wall of water that rushes far inland and causes devastating damage
7) Tsunamis can be devastating for buildings built in coastal areas
386 अति Fire
When the fire following an earthquake starts it becomes difficult to extinguish it since a strong
earthquake is accompanied by the loss of water supply and traffic jams Therefore the
earthquake damage increases with the earthquake-induced fire in addition to the damage to
buildings directly due to earthquakes
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अधयाय Chapter ndash 4
भको पी जोन और भको प का मापन Seismic Zone and Measurement of Earthquake
41 भको पी जोन Seismic Zone
Due to convective flow of mantle material crust of Earth and some portion of mantle slide on hot
molten outer core This sliding of Earthrsquos mass takes place in pieces called Tectonic Plates The
surface of the Earth consists of seven major tectonic plates (Fig 41)
They are
1 Eurasian Plate
2 Indo-Australian Plate
3 Pacific Plate
4 North American Plate
5 South American Plate
6 African Plate
7 Antarctic Plate
India lies at the northwestern end of the Indo Australian Plate (Fig 42) This Plate is colliding
against the huge Eurasian Plate and going under the Eurasian Plate Three chief tectonic sub-
regions of India are
the mighty Himalayas along the north
the plains of the Ganges and other rivers and
the peninsula
Most earthquakes occur along the Himalayan plate boundary (these are inter-plate earthquakes)
but a number of earthquakes have also occurred in the peninsular region (these are intra-plate
earthquakes)
Fig 41 Major Tectonic Plates on the Earthrsquos surface
Fig 42 Geographical Layout and Tectonic Plate
Boundaries in India
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Bureau of Indian Standards [IS1893 (part ndash 1) 2002] based on various scientific inputs from a
number of agencies including earthquake data supplied by Indian Meteorological Department
(IMD) has grouped the country into four seismic zones viz Zone II III IV and V Of these
Zone V is rated as the most seismically prone region while Zone II is the least (Fig 43)
Indian Seismic code (IS 18932002) divides the country into four seismic zones based on the
expected intensity of shaking in future earthquake The four zones correspond to areas that have
potential for shaking intensity on MSK scale as shown in the table
Seismic Zone Intensity on MSK scale of total area
II (Low intensity zone) VI (or less) 43
III (Moderate intensity zone) VII 27
IV (Severe intensity zone) VIII 18
V (Very Severe intensity zone) IX (and above) 12
Fig 43 Map showing Seismic Zones of India [IS 1893 (Part 1) 2002]
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42 भको प का मापन Measurement of Earthquake
421 मापन उपकरण Measuring Instruments
Seismograph The instrument that measures earthquake shaking is known as a seismograph
(Fig 44) It has three components ndash
Sensor ndash It consists of pendulum mass
string magnet and support
Recorder ndash It consists of drum pen and
chart paper
Timer ndash It consists of the motor that rotates
the drum at constant speed
Seismoscopes Some instruments that do not
have a timer device provide only the maximum
extent (or scope) of motion during the
earthquake
Digital instruments The digital instruments using modern computer technology records the
ground motion on the memory of the microprocessor that is in-built in the instrument
Note The analogue instruments have evolved over time but today digital instruments are more
commonly used
422 मापन क सकल Scale of Measurement
The Richter Magnitude Scale (also called Richter scale) assigns a magnitude number to quantify
the energy released by an earthquake Richter scale is a base 10 logarithmic scale which defines
magnitude as the logarithm of the ratio of the amplitude of the seismic wave to an arbitrary minor
amplitude
The magnitude M of an Earthquake is defined as
M = log10 A - log10 A0
Where
A = Recorded trace amplitude for that earthquake at a given distance as written by a
standard type of instrument (say Wood Anderson instrument)
A0 = Same as A but for a particular earthquake selected as standard
This number M is thus independent of distance between the epicentre and the station and is a
characteristic of the earthquake The standard shock has been defined such that it is low enough
to make the magnitude of most of the recorded earthquakes positive and is assigned a magnitude
of zero Thus if A = A0
Fig 44 Schematic of Early Seismograph
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M = log10 A0 - log10 A0 = 0
Standard shock of magnitude zero It is defined as one that records peak amplitude of one
thousandths of a millimetre at a distance of 100 km from the epicentre
1) Zero magnitude does not mean that there is no earthquake
2) Magnitude of an earthquake can be a negative number also
3) An earthquake that records peak amplitude of 1 mm on a standard seismograph at 100 km
will have its magnitude as
M = log10 (1) - log10 (10-3
)= 0 ndash (-3) = 3
Magnitude of a local earthquake It is defined as the logarithm to base 10 of the maximum
seismic wave amplitude (in thousandths of a mm) recorded on Wood Anderson seismograph at a
distance of 100 kms from the earthquake epicentre
1) With increase in magnitude by 10 the energy released by an earthquake increases by a
factor of about 316
2) A magnitude 80 earthquake releases about 316 times the energy released by a magnitude
70 earthquake or about 1000 times the energy released by a 60 earthquake
3) With increase in magnitude by 02 the energy released by the earthquake doubles
43 भको प पररमाण सकल क परकार Types of Earthquake Magnitude Scales
Several scales have historically been described as the ldquoRitcher Scalerdquo The Ritcher local
magnitude (ML) is the best known magnitude scale but it is not always the most appropriate scale
for description of earthquake size The Ritcher local magnitude does not distinguish between
different types of waves
At large epicentral distances body waves have usually been attenuated and scattered sufficiently
that the resulting motion is dominated by surface waves
Other magnitude scales that base the magnitude on the amplitude of a particular wave have been
developed They are
a) Surface Wave Magnitude (MS)
b) Body Wave Magnitude (Mb)
c) Moment Magnitude (Mw)
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431 सिि लिर पररमाण Surface Wave Magnitude (MS)
The surface wave magnitude (Gutenberg and Ritcher 1936) is a worldwide magnitude scale
based on the amplitude of Rayleigh waves with period of about 20 sec The surface wave
magnitude is obtained from
MS = log A + 166 log Δ + 20
Where A is the maximum ground displacement in micrometers and Δ is the epicentral distance of
the seismometer measured in degrees (3600 corresponding to the circumference of the earth)
The surface wave magnitude is most commonly used to describe the size of shallow (less than
about 70 km focal depth) distant (farther than about 1000 km) moderate to large earthquakes
432 बॉिी लिर पररमाण Body Wave Magnitude (Mb)
For deep-focus earthquakes surface waves are often too small to permit reliable evaluation of the
surface wave magnitude The body wave magnitude (Gutenberg 1945) is a worldwide magnitude
scale based on the amplitude of the first few cycles of p-waves which are not strongly influenced
by the focal depth (Bolt 1989) The body wave magnitude can be expressed as
Mb = log A ndash log T + 001Δ + 59
Where A is the p-wave amplitude in micrometers and T is the period of the p-wave (usually
about one sec)
Saturation
For strong earthquakes the measured
ground-shaking characteristics become
less sensitive to the size of the
earthquake than the smaller earthquakes
This phenomenon is referred to as
saturation (Fig 45)
The body wave and the Ritcher local
magnitudes saturate at magnitudes of 6
to 7 and the surface wave magnitude
saturates at about Ms = 8
To describe the size of a very large
earthquake a magnitude scale that does
not depend on ground-shaking levels
and consequently does not saturate
would be desirable
Fig 45 Saturation of various magnitude scale Mw (Moment
Magnitude) ML (Ritcher Local Magnitude) MS (Surface Wave
Magnitude) mb (Short-period Body Wave Magnitude) mB
(Long-period Body Wave Magnitude) and MJMA (Japanese
Meteorological Agency Magnitude)
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433 पल पररमाण Moment Magnitude (Mw)
The only magnitude scale that is not subject to saturation is the moment magnitude
The moment magnitude is given by
Mw = [(log M0)15] ndash 107
Where M0 is the seismic moment in dyne-cm
44 भको प िीवरिा Earthquake Intensity
Earthquake magnitude is simply a measure of the size of the earthquake reflecting the elastic
energy released by the earthquake It is usually referred by a certain real number on the Ritcher
scale (eg magnitude 65 earthquake)
On the other hand earthquake intensity indicates the extent of shaking experienced at a given
location due to a particular earthquake It is usually referred by a Roman numeral on the
Modified Mercalli Intensity (MMI) scale as given below
I Not felt except by a very few under especially favourable circumstances
II Felt by only a few persons at rest especially on upper floors of buildings delicately
suspended objects may swing
III Felt quite noticeably indoors especially on upper floors of buildings but many people
do not recognize it as an earthquake standing motor cars may rock slightly vibration
like passing of truck duration estimated
IV During the day felt indoors by many outdoors by few at night some awakened
dishes windows doors disturbed walls make cracking sound sensation like heavy
truck striking building standing motor cars rocked noticeably
V Felt by nearly everyone many awakened some dishes windows etc broken a few
instances of cracked plaster unstable objects overturned disturbances of trees piles
and other tall objects sometimes noticed pendulum clocks may stop
VI Felt by all many frightened and run outdoors some heavy furniture moved a few
instances of fallen plaster or damaged chimneys damage slight
VII Everybody runs outdoors damage negligible in buildings of good design and
construction slight to moderate in well-built ordinary structures considerable in
poorly built or badly designed structures some chimneys broken noticed by persons
driving motor cars
VIII Damage slight in specially designed structures considerable in ordinary substantial
buildings with partial collapse great in poorly built structures panel walls thrown out
of frame structures fall of chimneys factory stacks columns monuments walls
heavy furniture overturned sand and mud ejected in small amounts changes in well
water persons driving motor cars disturbed
IX Damage considerable in specially designed structures well-designed frame structures
thrown out of plumb great in substantial buildings with partial collapse buildings
shifted off foundations ground cracked conspicuously underground pipes broken
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X Some well-built wooden structures destroyed most masonry and frame structures
destroyed with foundations ground badly cracked rails bent landslides considerable
from river banks and steep slopes shifted sand and mud water splashed over banks
XI Few if any (masonry) structures remain standing bridges destroyed broad fissures in
ground underground pipelines completely out of service earth slumps and land slips
in soft ground rails bent greatly
XII Damage total practically all works of construction are damaged greatly or destroyed
waves seen on ground surface lines of sight and level are destroyed objects thrown
into air
441 MSK िीवरिा सकल MSK Intensity Scale
The MSK intensity scale is quite comparable to the Modified Mercalli intensity scale but is more
convenient for application in field and is widely used in India In assigning the MSK intensity
scale at a site due attention is paid to
Type of Structures (Table ndash A)
Percentage of damage to each type of structure (Table ndash B)
Grade of damage to different types of structures (Table ndash C)
Details of Intensity Scale (Table ndash D)
The main features of MSK intensity scale are as follows
Table ndash A Types of Structures (Buildings)
Type of
Structures
Definitions
A Building in field-stone rural structures unburnt ndash brick houses clay houses
B Ordinary brick buildings buildings of large block and prefabricated type half
timbered structures buildings in natural hewn stone
C Reinforced buildings well built wooden structures
Table ndash B Definition of Quantity
Quantity Percentage
Single few About 5 percent
Many About 50 percent
Most About 75 percent
Table ndash C Classification of Damage to Buildings
Grade Definitions Descriptions
G1 Slight damage Fine cracks in plaster fall of small pieces of plaster
G2 Moderate damage Small cracks in plaster fall of fairly large pieces of plaster
pantiles slip off cracks in chimneys parts of chimney fall down
G3 Heavy damage Large and deep cracks in plaster fall of chimneys
G4 Destruction Gaps in walls parts of buildings may collapse separate parts of
the buildings lose their cohesion and inner walls collapse
G5 Total damage Total collapse of the buildings
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Table ndash D Details of Intensity Scale
Intensity Descriptions
I Not noticeable The intensity of the vibration is below the limits of sensibility
the tremor is detected and recorded by seismograph only
II Scarcely noticeable
(very slight)
Vibration is felt only by individual people at rest in houses
especially on upper floors of buildings
III Weak partially
observed only
The earthquake is felt indoors by a few people outdoors only in
favourable circumstances The vibration is like that due to the
passing of a light truck Attentive observers notice a slight
swinging of hanging objects somewhat more heavily on upper
floors
IV Largely observed The earthquake is felt indoors by many people outdoors by few
Here and there people awake but no one is frightened The
vibration is like that due to the passing of a heavily loaded truck
Windows doors and dishes rattle Floors and walls crack
Furniture begins to shake Hanging objects swing slightly Liquid
in open vessels are slightly disturbed In standing motor cars the
shock is noticeable
V Awakening
a) The earthquake is felt indoors by all outdoors by many Many
people awake A few run outdoors Animals become uneasy
Buildings tremble throughout Hanging objects swing
considerably Pictures knock against walls or swing out of
place Occasionally pendulum clocks stop Unstable objects
overturn or shift Open doors and windows are thrust open
and slam back again Liquids spill in small amounts from
well-filled open containers The sensation of vibration is like
that due to heavy objects falling inside the buildings
b) Slight damages in buildings of Type A are possible
c) Sometimes changes in flow of springs
VI Frightening
a) Felt by most indoors and outdoors Many people in buildings
are frightened and run outdoors A few persons loose their
balance Domestic animals run out of their stalls In few
instances dishes and glassware may break and books fall
down Heavy furniture may possibly move and small steeple
bells may ring
b) Damage of Grade 1 is sustained in single buildings of Type B
and in many of Type A Damage in few buildings of Type A
is of Grade 2
c) In few cases cracks up to widths of 1cm possible in wet
ground in mountains occasional landslips change in flow of
springs and in level of well water are observed
VII Damage of buildings
a) Most people are frightened and run outdoors Many find it
difficult to stand The vibration is noticed by persons driving
motor cars Large bells ring
b) In many buildings of Type C damage of Grade 1 is caused in
many buildings of Type B damage is of Grade 2 Most
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buildings of Type A suffer damage of Grade 3 few of Grade
4 In single instances landslides of roadway on steep slopes
crack inroads seams of pipelines damaged cracks in stone
walls
c) Waves are formed on water and is made turbid by mud stirred
up Water levels in wells change and the flow of springs
changes Sometimes dry springs have their flow resorted and
existing springs stop flowing In isolated instances parts of
sand and gravelly banks slip off
VIII Destruction of
buildings
a) Fright and panic also persons driving motor cars are
disturbed Here and there branches of trees break off Even
heavy furniture moves and partly overturns Hanging lamps
are damaged in part
b) Most buildings of Type C suffer damage of Grade 2 and few
of Grade 3 Most buildings of Type B suffer damage of Grade
3 Most buildings of Type A suffer damage of Grade 4
Occasional breaking of pipe seams Memorials and
monuments move and twist Tombstones overturn Stone
walls collapse
c) Small landslips in hollows and on banked roads on steep
slopes cracks in ground up to widths of several centimetres
Water in lakes becomes turbid New reservoirs come into
existence Dry wells refill and existing wells become dry In
many cases change in flow and level of water is observed
IX General damage of
buildings
a) General panic considerable damage to furniture Animals run
to and fro in confusion and cry
b) Many buildings of Type C suffer damage of Grade 3 and a
few of Grade 4 Many buildings of Type B show a damage of
Grade 4 and a few of Grade 5 Many buildings of Type A
suffer damage of Grade 5 Monuments and columns fall
Considerable damage to reservoirs underground pipes partly
broken In individual cases railway lines are bent and
roadway damaged
c) On flat land overflow of water sand and mud is often
observed Ground cracks to widths of up to 10 cm on slopes
and river banks more than 10 cm Furthermore a large
number of slight cracks in ground falls of rock many
landslides and earth flows large waves in water Dry wells
renew their flow and existing wells dry up
X General destruction of
building
a) Many buildings of Type C suffer damage of Grade 4 and a
few of Grade 5 Many buildings of Type B show damage of
Grade 5 Most of Type A have destruction of Grade 5
Critical damage to dykes and dams Severe damage to
bridges Railway lines are bent slightly Underground pipes
are bent or broken Road paving and asphalt show waves
b) In ground cracks up to widths of several centimetres
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sometimes up to 1m Parallel to water courses occur broad
fissures Loose ground slides from steep slopes From river
banks and steep coasts considerable landslides are possible
In coastal areas displacement of sand and mud change of
water level in wells water from canals lakes rivers etc
thrown on land New lakes occur
XI Destruction
a) Severe damage even to well built buildings bridges water
dams and railway lines Highways become useless
Underground pipes destroyed
b) Ground considerably distorted by broad cracks and fissures
as well as movement in horizontal and vertical directions
Numerous landslips and falls of rocks The intensity of the
earthquake requires to be investigated specifically
XII Landscape changes
a) Practically all structures above and below ground are greatly
damaged or destroyed
b) The surface of the ground is radically changed Considerable
ground cracks with extensive vertical and horizontal
movements are observed Falling of rock and slumping of
river banks over wide areas lakes are dammed waterfalls
appear and rivers are deflected The intensity of the
earthquake requires to be investigated specially
442 तवतभनन सकलो ो की िीवरिा मलो ो की िलना Comparison of Intensity Values of
Different Scales
443 तवतभनन पररमाण और िीवरिा क भको प का परभाव Effect of Earthquake of various
Magnitude and Intensity
The following describes the typical effects of earthquakes of various magnitudes near the
epicenter The values are typical only They should be taken with extreme caution since intensity
and thus ground effects depend not only on the magnitude but also on the distance to the
epicenter the depth of the earthquakes focus beneath the epicenter the location of the epicenter
and geological conditions (certain terrains can amplify seismic signals)
Fig 45 Comparison of Intensity Values of Different Scales
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Magnitude Description Mercalli
intensity
Average earthquake effects Average
frequency of
occurrence
(estimated)
10-19 Micro I Micro earthquakes not felt or felt rarely
Recorded by seismographs
Continualseveral
million per year
20-29 Minor I to II Felt slightly by some people No damage to
buildings
Over one million
per year
30-39 III to IV Often felt by people but very rarely causes
damage Shaking of indoor objects can be
noticeable
Over 100000 per
year
40-49 Light IV to VI Noticeable shaking of indoor objects and
rattling noises Felt by most people in the
affected area Slightly felt outside
Generally causes none to minimal damage
Moderate to significant damage very
unlikely Some objects may fall off shelves
or be knocked over
10000 to 15000
per year
50-59 Moderate VI to
VIII
Can cause damage of varying severity to
poorly constructed buildings At most none
to slight damage to all other buildings Felt
by everyone
1000 to 1500 per
year
60-69 Strong VII to X Damage to a moderate number of well-built
structures in populated areas Earthquake-
resistant structures survive with slight to
moderate damage Poorly designed
structures receive moderate to severe
damage Felt in wider areas up to hundreds
of mileskilometers from the epicenter
Strong to violent shaking in epicentral area
100 to 150 per
year
70-79 Major VIII or
Greater
Causes damage to most buildings some to
partially or completely collapse or receive
severe damage Well-designed structures
are likely to receive damage Felt across
great distances with major damage mostly
limited to 250 km from epicenter
10 to 20 per year
80-89 Great Major damage to buildings structures
likely to be destroyed Will cause moderate
to heavy damage to sturdy or earthquake-
resistant buildings Damaging in large
areas Felt in extremely large regions
One per year
90 and
greater
At or near total destruction ndash severe damage
or collapse to all buildings Heavy damage
and shaking extends to distant locations
Permanent changes in ground topography
One per 10 to 50
years
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45 भको प तनगरानी और सवाओो क तलए एजतसयो ो Agencies for Earthquake Monitoring and
Services
Centre for Seismology (CS) in Indian Meteorological Department (IMD) under Ministry of
Earth Sciences is nodal agency of Government of India dealing with various activities in
the field of seismology and allied disciplines and is responsible for monitoring seismic
activity in and around the country
The major activities currently being pursued by the Centre for Seismology (CS) include
a) Earthquake monitoring on 24X7 basis including real time seismic monitoring for early
warning of tsunamis
b) Operation and maintenance of national seismological network and local networks
c) Seismological data centre and information services
d) Seismic hazard and risk related studies
e) Field studies for aftershock swarm monitoring site response studies
f) Earthquake processes and modelling etc
These activities are being managed by various unitsgroups of the Centre for Seismology
(CS) as detailed below
1) Centre for Seismology (CS) is maintaining a country wide National Seismological
Network (NSN) consisting of a total of 82 seismological stations spread over the
entire length and breadth of the country This includes
a) 16-station V-SAT based digital seismic telemetry system around National Capital
Territory (NCT) of Delhi
b) 20-station VSAT based real time seismic monitoring network in North East region
of the country
(c) 17-station Real Time Seismic Monitoring Network (RTSMN) to monitor and
report large magnitude under-sea earthquakes capable of generating tsunamis on
the Indian coastal regions
2) The remaining stations are of standalone analog type
3) A Control Room is in operation on a 24X7 basis at premises of IMD Headquarters in
New Delhi with state-of-the art facilities for data collection processing and
dissemination of information to the concerned user agencies
4) India represented by CSIMD is a permanent Member of the International
Seismological Centre (ISC) UK
5) Seismological Bulletins of CSIMD are shared regularly with International
Seismological Centre (ISC) UK for incorporation in the ISCs Monthly Seismological
Bulletins which contain information on earthquakes occurring all across the globe
6) Towards early warning of tsunamis real-time continuous seismic waveform data of
three IMD stations viz Portblair Minicoy and Shillong is shared with global
community through IRIS (Incorporated Research Institutions of Seismology)
Washington DC USA
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अधयाय Chapter ndash 5
भवन म भको प परतिरोध म सधार क तलए सामानय तसदाोि General Principle for improving Earthquake Resistance in Building
51 िलकापन Lightness
Since the earthquake force is a function of mass the building should be as light as possible
consistent with structural safety and functional requirements Roofs and upper storeys of
buildings in particular should be designed as light as possible
52 तनमायण की तनरोिरिा Continuity of Construction
As far as possible all parts of the building should be tied together in such a manner that
the building acts as one unit
For integral action of building roof and floor slabs should be continuous throughout as
far as possible
Additions and alterations to the structures should be accompanied by the provision of
positive measures to establish continuity between the existing and the new construction
53 परोजककटोग एवो ससिि पाटटयस Projecting and Suspended Parts
Projecting parts should be avoided as far as possible If the projecting parts cannot be
avoided they should be properly reinforced and firmly tied to the main structure
Ceiling plaster should preferably be avoided When it is unavoidable the plaster should
be as thin as possible
Suspended ceiling should be avoided as far as possible Where provided they should be
light and adequately framed and secured
54 भवन की आकति Shape of Building
In order to minimize torsion and stress concentration the building should have a simple
rectangular plan
It should be symmetrical both with respect to mass and rigidity so that the centre of mass
and rigidity of the building coincide with each other
It will be desirable to use separate blocks of rectangular shape particularly in seismic
zones V and IV
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55 सतवधा जनक तबकडोग लआउट Preferred Building Layouts
Buildings having plans with shapes like L T E and Y shall preferably be separated into
rectangular parts by providing separation sections at appropriate places Typical examples are
shown in Fig 51
56 तवतभनन तदशाओो म शककत Strength in Various Directions
The structure shall have adequate strength against earthquake effects along both the horizontal
axes considering the reversible nature of earthquake forces
57 नी ोव Foundations
For the design of foundations the provisions of IS 1904 1986 in conjunctions with IS
1893 1984 shall generally be followed
The sub-grade below the entire area of the building shall preferably be of the same type of
the soil Wherever this is not possible a suitably located separation or crumple section shall
be provided
Loose fine sand soft silt and expansive clays should be avoided If unavoidable the
building shall rest either on a rigid raft foundation or on piles taken to a firm stratum
However for light constructions the following measures may be taken to improve the soil
on which the foundation of the building may rest
a) Sand piling and b) Soil stabilization
Structure shall not be founded on loose soil which will subside or liquefy during an
earthquake resulting in large differential settlement
58 छि एवो मोतजल Roofs and Floors
581 सपाट छि या फशय Flat roof or floor
Flat roof or floor shall not preferably be made of terrace of ordinary bricks supported on steel
timber or reinforced concrete joists nor they shall be of a type which in the event of an
earthquake is likely to be loosened and parts of all of which may fall If this type of construction
cannot be avoided the joists should be blocked at ends and bridged at intervals such that their
spacing is not altered during an earthquake
Fig 51 Typical Shapes of Building with Separation Sections [IS 4326 1993]
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582 ढलान वाली छि Pitched Roofs
For pitched roofs corrugated iron or asbestos sheets should be used in preference to
country Allahabad or Mangalore tiles or other loose roofing units
All roofing materials shall be properly tied to the supporting members
Heavy roofing materials should generally be avoided
583 सोवि छि Pent Roofs
All roof trusses should be supported on and fixed to timber band reinforced concrete band or
reinforced brick band The holding down bolts should have adequate length as required for
earthquake and wind forces
Where a trussed roof adjoins a masonry gable the ends of the purlins should be carried on and
secured to a plate or bearer which should be adequately bolted to timber reinforced concrete or
reinforced brick band at the top of gable end masonry
- At tie level all the trusses and the gable end should be provided with diagonal braces in plan
so as to transmit the lateral shear due to earthquake force to the gable walls acting as shear
walls at the ends
NOTE ndash Hipped roof in general have shown better structural behaviour during earthquakes than gable
ended roofs
584 जक मिराब Jack Arches
Jack arched roofs or floors where used should be provided with mild steel ties in all spans along
with diagonal braces in plan to ensure diaphragm actions
59 सीतढ़याो Staircases
The interconnection of the stairs with the adjacent floors should be appropriately treated by
providing sliding joints at the stairs to eliminate their bracing effect on the floors
Ladders may be made fixed at one end and freely resting at the other
Large stair halls shall preferably be separated from rest of the building by means of
separation or crumple section
Three types of stair construction may be adopted as described below
591 अलग सीतढ़याो Separated Staircases
One end of the staircase rests on a wall and the other end is carried by columns and beams which
have no connection with the floors The opening at the vertical joints between the floor and the
staircase may be covered either with a tread plate attached to one side of the joint and sliding on
the other side or covered with some appropriate material which could crumple or fracture during
an earthquake without causing structural damage
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The supporting members columns or walls are
isolated from the surrounding floors by means of
separation or crumple sections A typical
example is shown in Fig 52
592 तबलट-इन सीतढ़याो Built-in Staircase
When stairs are built monolithically with floors they can be protected against damage by
providing rigid walls at the stair opening An arrangement in which the staircase is enclosed by
two walls is given in Fig 53 (a) In such cases the joints as mentioned in respect of separated
staircases will not be necessary
The two walls mentioned above enclosing the staircase shall extend through the entire height of
the stairs and to the building foundations
Fig 53 (a) Rigidly Built-In Staircase [IS 4326 1993]
Fig 52 Separated Staircase
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593 सलाइतिोग जोड़ो ो वाली सीतढ़याो Staircases with Sliding Joints
In case it is not possible to provide rigid walls around stair openings for built-in staircase or to
adopt the separated staircases the staircases shall have sliding joints so that they will not act as
diagonal bracing (Fig 53 (b))
510 बॉकस परकार तनमायण Box Type Construction
This type of construction consists of prefabricated or in-situ masonry wall along with both the
axes of the building The walls support vertical loads and also act as shear walls for horizontal
loads acting in any direction All traditional masonry construction falls under this category In
prefabricated wall construction attention should be paid to the connections between wall panels
so that transfer of shear between them is ensured
511 अति सरकषा Fire Safety
Fire frequently follows an earthquake and therefore buildings should be constructed to make
them fire resistant in accordance with the provisions of relevant Indian Standards for fire safety
The relevant Indian Standards are IS 1641 1988 IS 1642 1989 IS 1643 1988 IS 1644 1988
and IS 1646 1986
Fig 53 (b) Staircase with Sliding Joint
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अधयाय Chapter ndash 6
भको प क दौरान आर सी भवनो ो क परदशयन पर सटरकचरल अतनयतमििाओो का परभाव Effect of Structural Irregularities on Performance of RC Buildings during Earthquakes
61 सटरकचरल अतनयतमििाओो का परभाव Effect of Structural Irregularities
There are numerous examples of past earthquakes in which the cause of failure of reinforced
concrete building has been ascribed to irregularities in configurations
Irregularities are mainly categorized as
(i) Horizontal Irregularities
(ii) Vertical Irregularities
62 कषतिज अतनयतमििाएो Horizontal Irregularities
Horizontal irregularities refer to asymmetrical plan shapes (eg L- T- U- F-) or discontinuities
in the horizontal resisting elements (diaphragms) such as cut-outs large openings re-entrant
corners and other abrupt changes resulting in torsion diaphragm deformations stress
concentration
Table ndash 61 Definitions of Irregular Buildings ndash Plan Irregularities (Fig 61)
S
No
Irregularity Type and Description
(i) Torsion Irregularity To be considered when floor diaphragms are rigid in their own
plan in relation to the vertical structural elements that resist the lateral forces Torsional
irregularity to be considered to exist when the maximum storey drift computed with
design eccentricity at one end of the structures transverse to an axis is more than 12
times the average of the storey drifts at the two ends of the structure
Fig 61 (a)
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(ii) Re-entrant Corners Plan configurations of a structure and its lateral force resisting
system contain re-entrant corners where both projections of the structure beyond the re-
entrant corner are greater than 15 percent of its plan dimension in the given direction
Fig 61 (b)
(iii) Diaphragm Discontinuity Diaphragms with abrupt discontinuities or variations in
stiffness including those having cut-out or open areas greater than 50 percent of the
gross enclosed diaphragm area or changes in effective diaphragm stiffness of more than
50 percent from one storey to the next
Fig 61 (c)
(iv) Out-of-Plane Offsets Discontinuities in a lateral force resistance path such as out-of-
plane offsets of vertical elements
Fig 61 (d)
(v) Non-parallel Systems The vertical elements
resisting the lateral force are not parallel to or
symmetric about the major orthogonal axes or the
lateral force resisting elements
Fig 61 (e)
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63 ऊरधायधर अतनयतमििाएो Vertical Irregularities
Vertical irregularities referring to sudden change of strength stiffness geometry and mass result
in irregular distribution of forces and or deformation over the height of building
Table ndash 62 Definition of Irregular Buildings ndash Vertical Irregularities (Fig 62)
S
No
Irregularity Type and Description
(i) a) Stiffness Irregularity ndash Soft Storey A soft storey is one in which the lateral stiffness is
less than 70 percent of that in the storey above or less than 80 percent of the average lateral
stiffness of the three storeys above
b) Stiffness Irregularity ndash Extreme Soft Storey A extreme soft storey is one in which the
lateral stiffness is less than 60 percent of that in the storey above or less than 70 percent of
the average stiffness of the three storeys above For example buildings on STILTS will fall
under this category
Fig 62 (a)
(ii) Mass Irregularity Mass irregularity shall be considered to exist where the seismic weight
of any storey is more than 200percent of that of its adjacent storeys The irregularity need
not be considered in case of roofs
Fig 62 (b)
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(iii) Vertical Geometric Irregularity Vertical geometric irregularity shall be considered to
exist where the horizontal dimension of the lateral force resisting system in any storey is
more than150 percent of that in its adjacent storey
Fig 62 (c)
(iv) In-Plane Discontinuity in Vertical Elements Resisting Lateral Force A in-plane offset of
the lateral force resisting elements greater than the length of those elements
Fig 62 (d)
(v) Discontinuity in Capacity ndash Weak Storey A weak storey is one in which the storey lateral
strength is less than 80 percent of that in the storey above The storey lateral strength is the
total strength of all seismic force resisting elements sharing the storey shear in the
considered direction
64 भवन तवनयास अतनयतमििाएो ndash सरसकयमए ववशलषण एव तनदमन क उपमय Building
Irregularities ndash Problems Analysis and Remedial Measures
The influence of irregularity on performance of building during earthquakes is presented to
account for the effects of these irregularities in analysis of problems and their solutions along
with the design
Vertical Geometric Irregularity when L2gt15 L1
In-Plane Discontinuity in Vertical Elements Resisting Weak Storey when Filt08Fi+ 1
Lateral Force when b gta
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Architectural problems Structural problems Remedial measures
Extreme heightdepth ratio
High overturning forces large drift causing non-structural damage foundation stability
Revive properties or special structural system
Extreme plan area Built-up large diaphragm forces Subdivide building by seismic joints
Extreme length depth ratio
Built-up of large lateral forces in perimeter large differences in resistance of two axes Experience greater variations in ground movement and soil conditions
Subdivide building by seismic joints
Variation in perimeter strength-stiffness
Torsion caused by extreme variation in strength and stiffness
Add frames and disconnect walls or use frames and lightweight walls
False symmetry Torsion caused by stiff asymmetric core Disconnect core or use frame with non-structural core walls
Re-entrant corners Torsion stress concentrations at the notches
Separate walls uniform box centre box architectural relief diagonal reinforcement
Mass eccentricities Torsion stress concentrations Reprogram or add resistance around mass to balance resistance and mass
Vertical setbacks and reverse setbacks
Stress concentration at notch different periods for different parts of building high diaphragm forces to transfer at setback
Special structural systems careful dynamic analysis
Soft storey frame Causes abrupt changes of stiffness at point of discontinuity
Add bracing add columns braced
Variation in column stiffness
Causes abrupt changes of stiffness much higher forces in stiffer columns
Redesign structural system to balance stiffness
Discontinuous shear wall Results in discontinuities in load path and stress concentration for most heavily loaded elements
Primary concern over the strength of lower level columns and connecting beams that support the load of discontinuous frame
Weak column ndash strong beam
Column failure occurs before beam short column must try and accommodate storey height displacement
Add full walls to reduce column forces or detach spandrels from columns or use light weight curtain wall with frame
Modification of primary structure
Most serious when masonry in-fill modifies structural concept creation of short stiff columns result in stress concentration
Detach in-fill or use light-weight materials
Building separation (Pounding)
Possibility of pounding dependent on building period height drift distance
Ensure adequate separation assuming opposite building vibrations
Coupled Incompatible deformation between walls and links
Design adequate link
Random Openings Seriously degrade capacity at point of maximum force transfer
Careful designing adequate space for reinforcing design
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अधयाय Chapter ndash 7
भवन की िायनातमक तवशषिाएा Dynamic Characteristics of Building
71 िायनातमक तवशषिाएा Dynamic Characteristics
Buildings oscillate during earthquake shaking The oscillation causes inertia force to be induced
in the building The intensity and duration of oscillation and the amount of inertia force induced
in a building depend on features of buildings called dynamic characteristics of building
The important dynamic characteristics of buildings are
a) Modes of Oscillation
b) Damping
A mode of oscillation of a building is defined by associated Natural Period and Deformed Shape
in which it oscillates Every building has a number of natural frequencies at which it offers
minimum resistance to shaking induced by external effects (like earthquakes and wind) and
internal effects(like motors fixed on it) Each of these natural frequencies and the associated
deformation shape of a building constitute a Natural Mode of Oscillation
The mode of oscillation with the smallest natural frequency (and largest natural period) is called
the Fundamental Mode the associated natural period T1is called the Fundamental Natural
Period
72 पराकतिक अवतध Natural Period
Natural Period (Tn) of a building is the time taken by it to undergo one complete cycle of
oscillation It is an inherent property of a building controlled by its mass m and stiffness k These
three quantities are related by
Its unit is second (s)
73 पराकतिक आवततत Natural Frequency
The reciprocal (1Tn) of natural period of a building is called the Natural Frequency fn its unit is
Hertz (Hz)
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74 पराकतिक अवतध को परभातवि करन वाल कारक Factors influencing Natural Period
741 कठोरिा का परभाव Effect of Stiffness Stiffer buildings have smaller natural period
742 दरवयमान का परभाव Effect of Mass Heavier buildings have larger natural period
743 कॉलम अतभतवनयास का परभाव Effect of Column Orientation Buildings with larger
column dimension oriented in the direction reduces the translational natural period of oscillation
in that direction
Fig 72 Effect of Mass
Fig 71 Effect of Stiffness
Fig 73 Effect of Column Orientation
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744 भवन की ऊो चाई का परभाव Effect of Building Height Taller buildings have larger
natural period
745 Unreinforced तचनाई भराव का परभाव Effect of Unreinforced Masonry Infills Natural
Period of building is lower when the stiffness contribution of URM infill is considered
Fig 75 Effect of Building Height
Fig 74 Effect of Building Height
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75 Mode आकति Mode Shape
Mode shape of oscillation associated with a natural period of a building is the deformed shape of
the building when shaken at the natural period Hence a building has as many mode shapes as
the number of natural periods
The deformed shape of the building associated with oscillation at fundamental natural period is
termed its first mode shape Similarly the deformed shapes associated with oscillations at
second third and other higher natural periods are called second mode shape third mode shape
and so on respectively
Fundamental Mode Shape of Oscillation
As shown in Fig 76 there are three basic modes of oscillation namely
1 Pure translational along X-direction
2 Pure translational along Y-direction and
3 Pure rotation about Z-axis
Regular buildings
These buildings have pure mode shapesThe Basic modes of oscillation ie two translational and
one rotational mode shapes
Irregular buildings
These buildings that have irregular geometry non-uniform distribution of mass and stiffness in
plan and along the height have mode shapes which are a mixture of these pure mode shapes
Each of these mode shapes is independent implying it cannot be obtained by combining any or
all of the other mode shapes
a) Fundamental and two higher translational modes of oscillation along X-direction of a
five storey benchmark building First modes shape has one zero crossing of the un-deformed
position second two and third three
Fig 76 Basic modes of oscillation
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b) Diagonal modes of oscillation First three modes of oscillation of a building symmetric in
both directions in plan first and second are diagonal translational modes and third rotational
c) Effect of modes of oscillation on column bending Columns are severely damaged while
bending about their diagonal direction
Fig 77 Fundamental and two higher translational modes of oscillation
along X-direction of a five storey benchmark building
Fig 78 Diagonal modes of oscillation
Fig 79 Effect of modes of oscillation on column bending
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76 Mode आकतियो ो को परभातवि करन वाल कारक Factors influencing Mode Shapes
761 Effect of relative flexural stiffness of structural elements Fundamental translational
mode shape changes from flexural-type to shear-type with increase in beam flexural stiffness
relative to that of column
762 Effect of axial stiffness of vertical members Fundamental translational mode shape
changes from flexure-type to shear-type with increase in axial stiffness of vertical members
Fig 710 Effect of relative flexural stiffness of structural elements
Fig 711 Effect of axial stiffness of vertical members
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763 Effect of degree of fixity at member ends Lack of fixity at beam ends induces flexural-
type behaviour while the same at column bases induces shear-type behaviour to the fundamental
translational mode of oscillation
Fig 712 Effect of degree of fixity at member ends
764 Effect of building height Fundamental translational mode shape of oscillation does not
change significantly with increase in building height unlike the fundamental translational natural
period which does change
Fig 713 Effect of building height
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765 Influence of URM Infill Walls in Mode Shape of RC frame Buildings Mode shape of
a building obtained considering stiffness contribution of URM is significantly different from that
obtained without considering the same
77 सोरचना की परतितकरया Response of Structure
The earthquakes cause vibratory motion which is cyclic about the equilibrium The structural
response is vibratory (Dynamic) and it is cyclic about the equilibrium position of structure The
fundamental natural frequency of most civil engineering structures lie in the range of 01 sec to
30 sec or so This is also the range of frequency content of earthquake-generated ground
motions Hence the ground motion imparts considerable amount of energy to the structures
Initially the structure responds elastically to the ground motion however as its yield capacity is
exceeded the structure responds in an inelastic manner During the inelastic response stiffness
and energy dissipation properties of the structure are modified
Response of the structure to a given strong ground motion depends not only on the properties of
input ground motion but also on the structural properties
78 तिजाइन सकटर म Design Spectrum
The design spectrum is a design specification which is arrived at by considering all aspects The
design spectrum may be in terms of acceleration velocity or displacement
Fig 714 Influence of URM Infill Walls in Mode Shape of RC frame Buildings
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Since design spectrum is a specification for design it cannot be viewed in isolation without
considering the other factors that go into the design process One must concurrently specify
a) The procedure to calculate natural period of the structure
b) The damping to be used for a given type of structure
c) The permissible stresses and strains load factors etc
Unless this information is part of a design spectrum the design specification is incomplete
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अधयाय Chapter ndash 8
डिजमइन पमशवा बलो क तनधमारण क ललए कोि आधमररि िरीकम Code based Procedure for Determination of Design Lateral Loads
81 भको पी तिजाइन की तफलोसफ़ी Philosophy of Seismic Design
Design of earthquake effect is not termed as Earthquake Proof Design Actual forces that appear
on structure during earthquake are much greater than the design forces Complete protection
against earthquake of all size is not economically feasible and design based alone on strength
criteria is not justified Earthquake demand is estimated only based on concept of probability of
exceedance Design of earthquake effect is therefore termed as Earthquake Resistant Design
against the probable value of demand
Maximum Considered Earthquake (MCE) The earthquake corresponding to the Ultimate
Safety Requirement is often called as Maximum Considered Earthquake
Design Basis Earthquake (DBE) It is defined as the Maximum Earthquake that reasonably can
be expected to experience at the site during lifetime of structure
The philosophy of seismic design is to ensure that structures possess at least a minimum strength
to
(i) resist minor (lt DBE) which may occur frequently without damage
(ii) resist moderate earthquake (DBE) without significant structural damage through some
non-structural damage
(iii) resist major earthquake (MCE) without collapse
82 भको पी तवशलषण क तलए िरीक Methods for Seismic Analysis
The response of a structure to ground vibrations is a function of the nature of foundation soil
materials form size and mode of construction of structures and duration and characteristics of
ground motion Code specifies design forces for structures standing on rock or firm soils which
do not liquefy or slide due to loss of strength during ground motion
Analysis is carried out by
a- Dynamic analysis procedure [Clause 78 of IS 1893 (Part I) 2002]
b- Simplified method referred as Lateral Force Procedure [Clause 75 of IS 1893 (Part I)
2002] also recognized as Equivalent Lateral Force Procedure or Equivalent Static
Procedure in the literature
The main difference between the equivalent lateral force procedure and dynamic analysis
procedure lies in the magnitude and distribution of lateral forces over the height of the buildings
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In the dynamic analysis procedure the lateral forces are based on the properties of the natural
vibration modes of the building which are determined by the distribution of mass and stiffness
over height In the equivalent lateral force procedures the magnitude of forces is based on an
estimation of the fundamental period and on the distribution of forces as given by simple
formulae appropriate for regular buildings
83 िायनातमक तवशलषण Dynamic Analysis
Dynamic analysis shall be performed to obtain the design seismic force and its distribution to
different levels along the height of the building and to the various lateral load resisting elements
for the following buildings
a) Regular buildings ndash Those greater than 40 m in height in Zones IV and V and those greater
than 90 m in height in Zones II and III Modelling as per Para 7845 of IS 1893 (Part 1)
2002 can be used
b) Irregular buildings (as defined in Table ndash 61 and Table ndash 62 of Chapter - 6) ndash All framed
buildings higher than 12m in Zones IV and V and those greater than 40m in height in Zones
II and III
84 पारशय बल परतकरया Lateral Force Procedure
The random earthquake ground motions which cause the structure to vibrate can be resolved in
any three mutually perpendicular directions The predominant direction of ground vibration is
usually horizontal
The codes represent the earthquake-induced inertia forces in the form of design equivalent static
lateral force This force is called as the Design Seismic Base Shear VB VB remains the primary
quantity involved in force-based earthquake-resistant design of buildings
The Design Seismic Base Shear VB is given by
Where Ah = Design horizontal seismic coefficient for a structure
=
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Z = Zone Factor
It is for the Maximum Considered Earthquake (MCE) and service life of structure in a zone
Generally Design Basis Earthquake (DBE) is half of Maximum Considered Earthquake
(MCE) The factor 2 in the denominator of Z is used so as to reduce the MCE zone factor to
the factor for DBE
The value of Ah will not be taken less than Z2 whatsoever the value of IR
The value of Zone Factor is given in Table ndash 81
Table ndash 81 Zone Factor Z[IS 1893 (Part 1) 2002]
Seismic Zone II III IV V
Seismic Intensity Low Moderate Severe Very Severe
Zone Factor Z 010 016 024 036
I = Importance Factor
Value of importance factor depends upon the functional use of the structures characterized
by hazardous consequences of its failure post-earthquake functional needs historical value
or economic importance (as given in Table ndash 82)
Table ndash 82 Importance Factors I [IS 1893 (Part 1) 2002]
S
No
Structure Importance
Factor
(i) Important service and community buildings such as hospitals schools
monumental structures emergency buildings like telephone exchange
television stations radio stations railway stations fire station buildings
large community halls like cinemas assembly halls and subway stations
power stations
15
(ii) AU other buildings 10
Note
1 The design engineer may choose values of importance factor I greater than those
mentioned above
2 Buildings not covered in S No (i) and (ii) above may be designed for higher value of I
depending on economy strategy considerations like multi-storey buildings having
several residential units
3 This does not apply to temporary structures like excavations scaffolding etc of short
duration
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R = Response Reduction Factor
To make normal buildings economical design code allows some damage for reducing the
cost of construction This philosophy is introduced with the help of Response reduction
factor R
The ratio (IR) shall not be greater than 10
Depending on the perceived seismic damage performance of the structure by ductile or brittle
deformations the values of R1)
for buildings are given in Table ndash 83 below
Table ndash 83 Response Reduction Factor1)
R for Building Systems [IS 1893 (Part 1) 2002]
S No Lateral Load Resisting System R Building Frame Systems (i) Ordinary RC moment-resisting frame ( OMRF )
2) 30
(ii) Special RC moment-resisting frame ( SMRF )3)
50 (iii) Steel frame with
a) Concentric braces 40 b) Eccentric braces 50
(iv) Steel moment resisting frame designed as per SP 6 (6) 50 Building with Shear Walls
4)
(v) Load bearing masonry wall buildings5)
a) Unreinforced 15 b) Reinforced with horizontal RC bands 25 c) Reinforced with horizontal RC bands and vertical bars at cornersof
rooms and jambs of openings 30
(vi) Ordinary reinforced concrete shear walls6)
30 (vii) Ductile shear walls
7) 40
Buildings with Dual Systems8)
(viii) Ordinary shear wall with OMRF 30 (ix) Ordinary shear wall with SMRF 40 (x) Ductile shear wall with OMRF 45 (xi) Ductile shear wall with SMRF 50 1) The values of response reduction factor are to be used for buildings with lateral load resisting
elements and not just for the lateral load resisting elements built in isolation 2) OMRF (Ordinary Moment-Resisting Frame) are those designed and detailed as per IS 456 or
IS 800 but not meeting ductile detailing requirement as per IS 13920 or SP 6 (6) respectively 3) SMRF (Special Moment-Resisting Frame) defined in 4152
As per 4152 SMRF is a moment-resisting frame specially detailed to provide ductile behaviour and comply with the requirements given in IS 4326 or IS 13920 or SP 6 (6)
4) Buildings with shear walls also include buildings having shear walls and frames but where a) frames are not designed to carry lateral loads or b) frames are designed to carry lateral loads but do not fulfil the requirements of lsquodual
systemsrsquo 5) Reinforcement should be as per IS 4326 6) Prohibited in zones IV and V 7) Ductile shear walls are those designed and detailed as per IS 13920 8) Buildings with dual systems consist of shear walls ( or braced frames ) and moment resisting
frames such that a) the two systems are designed to resist the total design force in proportion to their lateral
stiffness considering the interaction of the dual system at all floor levels and b) the moment resisting frames are designed to independently resist at least 25 percent of the
design seismic base shear
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Sag = Average Response Acceleration Coefficient
Net shaking of a building is a combined effect of the energy carried by the earthquake at
different frequencies and the natural period (T) of the building Code reflects this by
introducing a structural flexibility factor (Sag) also termed as Design Acceleration
Coefficient
Design Acceleration Coefficient (Sag) corresponding to 5 damping for different soil
types normalized to Peak Ground Acceleration (PAG) corresponding to natural period (T)
of structure considering soil structure interaction given by Fig 81 and associated expression
given below
Table ndash 84 gives multiplying factors for obtaining spectral values for various other damping
Table ndash 84 Multiplying Factors for Obtaining Values for Other Damping [IS 1893 (Part 1) 2002]
Damping () 0 2 5 7 10 15 20 25 30
Factors 320 140 100 090 080 070 060 055 050
85 को पन की मौतलक पराकतिक अवतध Fundamental Natural Period of Vibration
The approximate fundamental natural period of vibration (Ta)in seconds of a moment-resisting
frame building without brick infill panels may be estimated by the empirical expression
Ta = 0075 h075
for RC frame building
= 0085 h075
for steel frame building
Where h = Height of building in m This excludes the basement storeys where
basement walls are connected with the ground floor deck or fitted between
the building columns But it includes the basement storeys when they are
not so connected
Fig 81 Response Spectra for Rock and Soil Sitesfor5 Damping [IS 1893 (Part 1) 2002]
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The approximate fundamental natural period of vibration (Ta) in seconds of all other buildings
including moment-resisting frame buildings with brick infill panels may be estimated by the
empirical expression
Where h = Height of building in m as defined above
d = Base dimension of the building at the plinth level in m along the
considered direction of the lateral force
86 तिजाइन पारशय बल Design Lateral Force
The total design lateral force or design seismic base shear (VB) along any principal direction shall
be determined by the following expression
Where Ah= Design horizontal acceleration spectrum value as per 642 using the
fundamental natural period Ta as per 76 in the considered direction of
vibration and
W= Seismic weight of the building
The design lateral force shall first be computed for the building as a whole This design lateral
force shall then be distributed to the various floor levels
The overall design seismic force thus obtained at each floor level shall then be distributed to
individual lateral load resisting elements depending on the floor diaphragm action
87 तिजाइन बल का तविरण Distribution of Design Force
871 Vertical Distribution of Base Shear to Different Floor Levels
The Design Seismic Base Shear (VB) as computed above shall be distributed along the height of
the building as per the following expression
Where
Qi= Design lateral force at floor i
Wi = Seismic weight of floor i
hi = Height of floor i measured from base and
n= Number of storeys in the building is the number of levels at which the masses are
located
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54
872 Distribution of Horizontal Design Lateral Force to Different Lateral Force Resisting
Elements
1 In case of buildings whose floors are capable of providing rigid horizontal diaphragm
action the total shear in any horizontal plane shall be distributed to the various vertical
elements of lateral force resisting system assuming the floors to be infinitely rigid in the
horizontal plane
2 In case of building whose floor diaphragms cannot be treated as infinitely rigid in their
own plane the lateral shear at each floor shall be distributed to the vertical elements
resisting the lateral forces considering the in-plane flexibility of the diaphragms
Notes
1 A floor diaphragm shall be considered to be flexible if it deforms such that the maximum
lateral displacement measured from the chord of the deformed shape at any point of the
diaphragm is more than 15 times the average displacement of the entire diaphragm
2 Reinforced concrete monolithic slab-beam floors or those consisting of prefabricated
precast elements with topping reinforced screed can be taken rigid diaphragms
88 तिजाइन उदािरण Design Example ndash To determine Base Shear and its distribution
along Height of Building
Exercise ndash 1 Determine the total base shear as per IS 1893(Part 1)2002 and distribute the base
shear along the height of building to be used as school building in Bhuj Gujrat and founded on
Medium Soil Basic parameters for design of building are as follows
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55
ELEVATION
Solution
Basic Data
Following basic data is considered for analysis
i) Grade of Concrete M-25
ii) Grade of Steel Fe ndash 415 Tor Steel
iii) Density of Concrete 25 KNm3
iv) Density of Brick Wall 20 KNm3
v) Live Load for Roof 15 KNm2
vi) Live Load for Floor 50 KNm2
vii) Slab Thickness 150 mm
viii) Beam Size
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(a) 500 m Span 250 mm X 600 mm
(b) 400 m Span 250 mm X 550 mm
(c) 200 m Span 250 mm X 400 mm
ix) Column Size
(a) For 500 m Span 300 mm X 600 mm
(b) For 200 m Span 300 mm X 500 mm
Load Calculations
1 Dead Load Building is of G+4 Storeys
Approximate Covered Area of Building on GF = 30 X 8 = 240 m2
Approximate Covered Area of 1st 2
nd 3
rd amp 4
th Floor = 240 m
2
Total Floor Area = 5 X 240 = 1200 m2
Roof Area = 1 X 240 = 240 m2
(I) Slab
Self Wt of Slab = 015 X 25 = 375 KNm2
Wt of Floor Finish = 125 KNm2
------------------------------
Total = 500 KNm2
Dead Load of Slab per Floor = 240 X 5 = 1200 KN
Dead Load of Slab on Roof = 240 X 5 = 1200 KN
(II) Beam
Wt per m of 250 X 600 mm beam = 025 X 060 X 25 = 375 KNm
Wt per m of 250 X 550 mm beam = 025 X 055 X 25 = 344 KNm
Wt per m of 250 X 400 mm beam = 025 X 040 X 25 = 250 KNm
Weight of Beam per Floor
= (2 X 30 X 375) + (4 X 6 + 30) X 344 + (2 X 6 X 250)
= 225 + 18576 + 30 = 44076 KN [Say 44100 KN]
(III) Column
Wt per m of 300 X 600 mm column = 030 X 060 X 25 = 450 KNm
Wt per m of 300 X 500 mm column = 030 X 050 X 25 = 375 KNm
Weight of Column per Floor
= (12 X 3 X 450) + (6 X 3 X 375)
= 162 + 6750 = 22950 KN [Say 23000 KN]
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57
Walls
250 mm thick wall (including plaster) are provided Assuming 20 opening in the
wall ndash
Wt of Wall per m = 025 X 080 X 20 X 250
Wall Thickness Reduction Density Clear Height
= 1000 KNm
Wt of Parapet Wall per m = 0125 X 20 X 100 = 250 KNm
Wall Thickness Density Clear Height
Wt of Wall per Floor = 1000 X [30 X 3 + 2 X 2] = 940 KN
Wt of Wall at Roof = 250 X [30 X 2 + 8 X 2] = 190 KN
Total Dead Load ndash
(i) For Floor = Slab + Beam + Column + Wall
= 1200 + 441 + 230 + 940 = 2811 KN
(ii) For Roof = 1200 + 441 + 190 = 1831 KN
Slab Beam Parapet
2 Live Load Live Load on Floor = 40 KNm2
As per Table ndash 8 in Cl 731 of IS 1893 (Part 1)2002 ldquoage of Imposed Load to be
considered in Seismic Weight calculationrdquo
(i) Up to amp including 300 KNm2 = 25
(ii) Above 300 KNm2 = 50
Live Load on Floors to be = 200 KNm2 [ie 50 of 40 KNm
2]
considered for Earthquake Force
As per Cl 732 of IS 1893 (Part 1)2002 for calculating the design seismic force of the
structure the imposed load on roof need not be considered
Therefore Live Load on Roof = 000 KN
Seismic Weight due to Live Load
(i) For Floor = 240 X 2 = 480 KN
(ii) For Roof = 000 KN
3 Seismic Weight of Building
As per Cl 74 of IS 1893 (Part 1)2002
(i) For Floor = DL of Floor + LL on Floor
= 2811 + 480 = 3291 KN
(ii) For Roof = 1831 + 000 = 1831 KN
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58
Total Seismic Weight of Building = 5 X 3291 + 1 X 1831
W = 18286 KN
4 Determination of Base Shear
As per Cl 75 of IS 1893 (Part 1)2002 VB = Ah W
Where
VB = Base Shear
Ah = Design Horizontal Acceleration Spectrum
=
W = Seismic Wt of Building
Total height of Building above Ground Level = 1500 m
As per Cl 76 of IS 1893 (Part 1)2002 Fundamental Natural Period of Vibration for RC
Frame Building is
Ta = 0075 h075
= 0075 (15)075
= 0572 Sec
Average Response Acceleration Coefficient = 25
for 5 damping and Type II soil
Bhuj Gujrat is in Seismic Zone V
As per Table ndash 2 of IS 1893 (Part 1)2002
Zone Factor Z = 036
As per Table ndash 6 of IS 1893 (Part 1)2002
Impedance Factor I = 150
As per Table ndash 7 of IS 1893 (Part 1)2002
Response Reduction Factor for Ordinary R = 300
RC Moment-resisting Frame (OMRF) Building
Ah =
= (0362) X (1530) X (25)
= 0225
Base Shear VB = Ah W
= 0225 X 18286
= 411435 KN [Say 411400 KN]
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5 Vertical Distribution of Base Shear to Different Floors Levels
As per Cl 771 of IS 1893 (Part 1)2002
Where
Qi= Design lateral force at floor i
Wi = Seismic weight of floor i
hi = Height of floor i measured from base and
n= Number of storeys in the building is the number of levels at which the masses are
located
VB = 4114 KN
Storey
No
Mass
No
Wi hi Wi hi2
f =
Qi = VB x f
(KN)
Vi
(KN)
Roof 1 1831 18 593244 0268 1103 1103
4th
Floor 2 3291 15 740475 0333 1370 2473
3rd
Floor 3 3291 12 473904 0213 876 3349
2nd
Floor 4 3291 9 266571 0120 494 3843
1st Floor 5 3291 6 118476 0053 218 4061
Ground 6 3291 3 29619 0013 53 4114
= 2222289
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60
अधयाय Chapter ndash 9
ढााचागि सोरचना का तनमायण Construction of Framed Structure
91 गरतवाकषयण लोतिोग और भको प लोतिोग म आर सी तबकडोग का वयविार Behaviour of RC
Building in Gravity Loading and Earthquake Loading
In recent times reinforced concrete buildings have become common in India particularly in
towns and cities A typical RC building consists of horizontal members (beams and slabs) and
vertical members (columns and walls) The system is supported by foundations that rest on
ground The RC frame participates in resisting the gravity and earthquake forces as illustrated in
Fig 91
Gravity Loading
1 Load due to self weight and contents on buildings cause RC frames to bend resulting in
stretching and shortening at various locations
2 Tension is generated at surfaces that stretch
and compression at those that shorten
3 Under gravity loads tension in the beams is
at the bottom surface of the beam in the
central location and is at the top surface at
the ends
Earthquake Loading
1 It causes tension on beam and column faces
at locations different from those under
gravity loading the relative levels of this
tension (in technical terms bending
moment) generated in members are shown
in Figure
2 The level of bending moment due to
earthquake loading depends on severity of
shaking and can exceed that due to gravity
loading
3 Under strong earthquake shaking the beam
ends can develop tension on either of the
top and bottom faces
4 Since concrete cannot carry this tension
steel bars are required on both faces of
beams to resist reversals of bending
moment
5 Similarly steel bars are required on all faces of columns too
Fig 91 Earthquake shaking reverses tension and
compression in members ndash reinforcement is
required on both faces of members
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92 परबतलि को करीट इमारिो ो पर कषतिज भको प का परभाव Effect of Horizontal Earthquake Force
on RC Buildings
Earthquake shaking generates inertia forces in the building which are proportional to the
building mass Since most of the building mass is present at floor levels earthquake-induced
inertia forces primarily develop at the floor
levels These forces travel downwards -
through slab and beams to columns and walls
and then to the foundations from where they
are dispersed to the ground (Fig 92)
As inertia forces accumulate downwards from
the top of the building the columns and walls
at lower storeys experience higher earthquake-
induced forces and are therefore designed to be
stronger than those in storeys above
93 कषमिा तिजाइन सोकलपना Capacity Design Concept
(i) Let us take two bars of same length amp Cross-sectional area
1st bar ndash Made up of Brittle Material
2nd
bar ndash Made up of Ductile Material
(ii) Pull both the bars until they break
(iii) Plot the graph of bar force F versus bar
elongation Graph will be as given in Fig
93
(iv) It is observed that ndash
a) Brittle bar breaks suddenly on reaching its
maximum strength at a relatively small
elongation
b) Ductile bar elongates by a large amount
before it breaks
Materials used in building construction are steel
masonry and concrete Steel is ductile material
while masonry and concrete are brittle material
Capacity design concept ensures that the brittle
element will remain elastic at all loads prior to the
failure of ductile element Thus brittle mode of
failure ie sudden failure has been prevented
Fig 92 Total horizontal earthquake force in a
building increase downwards along its height
Fig 93 Tension Test on Materials ndash ductile
versus brittle materials
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The concept of capacity design is used to ensure post-yield ductile behaviour of a structure
having both ductile and brittle elements In this method the ductile elements are designed and
detailed for the design forces Then an upper-bound strength of the ductile elements is obtained
It is then expected that if the seismic force keeps increasing a point will come when these ductile
elements will reach their upper-bound strength and become plastic Clearly it is necessary to
ensure that even at that level of seismic force the brittle elements remain safe
94 लचीलापन और ऊजाय का अपवयय Ductility and Energy Dissipation
From strength point of view overdesigned structures need not necessarily demonstrate good
ductility By ductility of Moment Resisting Frames (MRF) one refers to the capacity of the
structure and its elements to undergo large deformations without loosing either strength or
stiffness It is important for a building in a seismic zone to be resilient ie absorb the shock from
the ground and dissipate this energy uniformly throughout the structure
In MRFs the dissipation of the input seismic energy takes place in the form of flexural yielding
and resulting in the formation of plastic moment hinges Due to cyclic nature of the flexural
effects both positive and negative plastic moment hinges may be formed
95 मजबि सतोभ ndash कमजोर बीम फलोसफ़ी lsquoStrong Column ndash Weak Beamrsquo Philosophy
Because beams are usually capable of developing large ductility than columns which are
subjected to significant compressive loads many building frames are designed based on the
lsquostrong column ndash weak beamrsquo philosophy Figure shows that for a frame designed according to
the lsquostrong column ndash weak beamrsquo philosophy to form a failure mechanism many more plastic
hinges have to be formed than a
frame designed according to the
ldquoweak column ndash strong beamrsquo
philosophy The frames designed
by the former approach dissipate
greater energy before failure
When this strategy is adopted in
design damage is likely to occur
first in beams When beams are
detailed properly to have large
ductility the building as a whole
can deform by large amounts
despite progressive damage caused
due to consequent yielding of
beams
Note If columns are made weaker they suffer severe local damage at the top and bottom of a
particular storey This localized damage can lead to collapse of a building although columns at
storeys above remain almost undamaged (Fig 94)
Fig 94 Two distinct designs of buildings that result in different
earthquake performancesndashcolumns should be stronger than beams
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For a building to remain safe during earthquake shaking columns (which receive forces from
beams) should be stronger than beams and foundations (which receive forces from columns)
should be stronger than columns
96 कठोर िायाफराम तकरया Rigid Diaphragm Action
When beams bend in the vertical direction during earthquakes these thin slabs bend along with them And when beams move with columns in the horizontal direction the slab usually forces the beams to move together with it In most buildings the geometric distortion of the slab is negligible in the horizontal plane this behaviour is known as the rigid diaphragm action This aspect must be considered during design (Fig 95)
97 सॉफट सटोरी तबकडोग क साथ ndash ओपन गराउोि सटोरी तबकडोग जो तक भको प क समय कमजोर िोिी ि
Building with Soft storey ndash Open Ground Storey Building that is vulnerable in
Earthquake
The buildings that have been constructed in recent times with a special feature - the ground storey is left open for the purpose of parking ie columns in the ground storey do not have any partition walls (of either masonry or RC) between them are called open ground storey buildings or buildings on stilts
An open ground storey building (Fig 96) having only columns in the ground storey and both partition walls and columns in the upper storeys have two distinct characteristics namely
(a) It is relatively flexible in the ground storey ie the relative horizontal displacement it undergoes in the ground storey is much larger than what each of the storeys above it does This flexible ground storey is also called soft storey
(b) It is relatively weak in ground storey ie
the total horizontal earthquake force it can carry in the ground storey is significantly smaller than what each of the storeys above it can carry Thus the open ground storey may also be a weak storey
Fig 95 Floor bends with the beam but moves all
columns at that level together
Fig 96 Upper storeys of open ground storey building
move together as a single block ndash such buildings are
like inverted pendulums
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The collapse of more than a hundred RC frame buildings with open ground storeys at
Ahmedabad (~225km away from epicenter) during the 2001 Bhuj earthquake has emphasized
that such buildings are extremely vulnerable under earthquake shaking
After the collapses of RC buildings in 2001 Bhuj earthquake the Indian Seismic Code IS 1893
(Part 1) 2002 has included special design provisions related to soft storey buildings
Firstly it specifies when a building should be considered as a soft and a weak storey building
Secondly it specifies higher design forces for the soft storey as compared to the rest of the
structure
The Code suggests that the forces in the columns
beams and shear walls (if any) under the action of
seismic loads specified in the code may be
obtained by considering the bare frame building
(without any infills) However beams and
columns in the open ground storey are required to
be designed for 25 times the forces obtained
from this bare frame analysis (Fig 97)
For all new RC frame buildings the best option is
to avoid such sudden and large decrease in stiffness
andor strength in any storey it would be ideal to
build walls (either masonry or RC walls) in the
ground storey also Designers can avoid dangerous
effects of flexible and weak ground storeys by
ensuring that too many walls are not discontinued
in the ground storey ie the drop in stiffness and
strength in the ground storey level is not abrupt due
to the absence of infill walls (Fig 98)
The existing open ground storey buildings need to be strengthened suitably so as to prevent them
from collapsing during strong earthquake shaking The owners should seek the services of
qualified structural engineers who are able to suggest appropriate solutions to increase seismic
safety of these buildings
971 भरी हई दीवार In-Fill Walls
When columns receive horizontal forces at floor
levels they try to move in the horizontal direction
but masonry walls tend to resist this movement
Due to their heavy weight and thickness these
walls attract rather large horizontal forces
However since masonry is a brittle material these
walls develop cracks once their ability to carry
horizontal load is exceeded Thus infill walls act
like sacrificial fuses in buildings they develop
Fig 99 Infill walls move together with the
columns under earthquake shaking
Fig 97 Open ground storey building ndashassumptions
made in current design practice are not consistent
with the actual structure
Fig 98 Avoiding open ground storey problem ndash
continuity of walls in ground storey is preferred
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65
cracks under severe ground shaking but help share the load of the beams and columns until
cracking Earthquake performance of infill walls is enhanced by mortars of good strength
making proper masonry courses and proper packing of gaps between RC frame and masonry
infill walls (Fig 99)
98 भको प क दौरान लघ कॉलम वाली इमारिो ो का वयविार Behavior of Buildings with Short
Columns during Earthquakes
During past earthquakes reinforced concrete (RC) frame buildings that have columns of different heights within one storey suffered more damage in the shorter columns as compared to taller columns in the same storey
Two examples of buildings with short columns are shown in Fig 910 ndash (a) buildings on a sloping ground and (b) buildings with a mezzanine floor
Poor behaviour of short columns is due to the fact that in an earthquake a tall column and a short column of same cross-section move horizontally by same amount
However the short column is stiffer as compared
to the tall column and it attracts larger earthquake
force Stiffness of a column means resistance to
deformation ndash the larger is the stiffness larger is
the force required to deform it If a short column is
not adequately designed for such a large force it
can suffer significant damage during an
earthquake This behaviour is called Short Column
Effect (Fig 911)
In new buildings short column effect should be
avoided to the extent possible during architectural
design stage itself When it is not possible to avoid
short columns this effect must be addressed in
structural design The IS13920-1993for ductile
detailing of RC structures requires special
confining reinforcement to be provided over the
full height of columns that are likely to sustain
short column effect
Fig 910 Buildings with short columns ndash two
explicit examples of common occurrences
Fig 911 Short columns are stiffer and attract larger
forces during earthquakes ndash this must be accounted
for in design
Fig 912 Details of reinforcement in a building with
short column effect in some columns ndashadditional
special requirements are given in IS13920- 1993 for
the short columns
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66
The special confining reinforcement (ie closely spaced closed ties) must extend beyond the
short column into the columns vertically above and below by a certain distance as shown in
Fig 912
In existing buildings with short columns different retrofit solutions can be employed to avoid
damage in future earthquakes Where walls of partial height are present the simplest solution is
to close the openings by building a wall of full height ndash this will eliminate the short column
effect If that is not possible short columns need to be strengthened using one of the well
established retrofit techniques The retrofit solution should be designed by a qualified structural
engineer with requisite background
99 भको प परतिरोधी इमारिो ो की लचीलापन आवशयकिाएा Ductility requirements of
Earthquake Resistant Buildings
The primary members of structure such as beams and columns are subjected to stress reversals
from earthquake loads The reinforcement provided shall cater to the needs of reversal of
moments in beams and columns and at their junctions
Earthquake motion often induces forces large enough to cause inelastic deformations in the
structure If the structure is brittle sudden failure could occur But if the structure is made to
behave ductile it will be able to sustain the earthquake effects better with some deflection larger
than the yield deflection by absorption of energy Therefore besides the design for strength of
the frame ductility is also required as an essential element for safety from sudden collapse during
severe shocks
The ductility requirements will be deemed to be satisfied if the conditions given as in the
following are achieved
1 For all buildings which are more than 3 storeys in height the minimum grade of concrete
shall be M20 ( fck = 20 MPa )
2 Steel reinforcements of grade Fe 415 (IS 1786 1985) or less only shall be used
However high strength deformed steel bars produced by the thermo-mechanical treatment
process of grades Fe 500 and Fe 550 having elongation more than 145 percent and conforming
to other requirements of IS 1786 1985 may also be used for the reinforcement
910 बीम तजनह आर सी इमारिो ो म भको प बलो ो का तवरोध करन क तलए िाला जािा ि Beams that
are required to resist Earthquake Forces in RC Buildings
In RC buildings the vertical and horizontal members (ie the columns and beams) are built
integrally with each other Thus under the action of loads they act together as a frame
transferring forces from one to another
Beams in RC buildings have two sets of steel reinforcement (Fig 913) namely
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67
(a) long straight bars (called longitudinal bars)
placed along its length and
(b) closed loops of small diameter steel bars (called
stirrups)placed vertically at regular intervals
along its full length
Beams sustain two basic types of failures namely
(i) Flexural (or Bending) Failure
As the beam sags under increased loading it can
fail in two possible ways (Fig 914)
If relatively more steel is present on the tension
face concrete crushes in compression this is
a brittle failure and is therefore undesirable
If relatively less steel is present on the
tension face the steel yields first (it keeps
elongating but does not snap as steel has
ability to stretch large amounts before it
snaps and redistribution occurs in the beam
until eventually the concrete crushes in
compression this is a ductile failure and
hence is desirable Thus more steel on
tension face is not necessarily desirable The
ductile failure is characterized with many
vertical cracks starting from the stretched
beam face and going towards its mid-depth
(ii) Shear Failure
A beam may also fail due to shearing action A shear crack is inclined at 45deg to the horizontal it
develops at mid-depth near the support and grows towards the top and bottom faces Closed loop
stirrups are provided to avoid such shearing action Shear damage occurs when the area of these
stirrups is insufficient Shear failure is brittle and therefore shear failure must be avoided in the
design of RC beams
Longitudinal bars are provided to resist flexural
cracking on the side of the beam that stretches
Since both top and bottom faces stretch during
strong earthquake shaking longitudinal steel bars
are required on both faces at the ends and on the
bottom face at mid-length (Fig 915)
Fig 914 Two types of damage in a beam flexure
damage is preferred Longitudinal bars resist the
tension forces due to bending while vertical stirrups
resist shear forces
Fig 913 Steel reinforcement in beams ndash stirrups
prevent longitudinal bars from bending outwards
Fig 915 Location and amount of longitudinal steel
bars in beams ndash these resist tension due to flexure
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Designing a beam involves the selection of its material properties (ie grades of steel bars
and concrete) and shape and size these are usually selected as a part of an overall design
strategy of the whole building
The amount and distribution of steel to be provided in the beam must be determined by
performing design calculations as per IS 456-2000 and IS 13920-1993
911 फलकसचरल ममबसय क तलए सामानय आवशयकिाएा General Requirements for Flexural
Members
These members shall satisfy the following requirements
The member shall preferably have a width-to-depth ratio of more than 03
The width of the member shall not be less than 200 mm
The depth D of the member shall preferably be not more than 14 of the clear span
The factored axial stress on the member under earthquake loading shall not exceed 01fck
9111 अनदधयय सदढीकरण Longitudinal Reinforcement
a) The top as well as bottom reinforcement shall consist of at least two bars throughout the
member length
b) The tension steel ratio on any face at any section shall not be less than ρmin = 024 where fck
and fy are in MPa
The positive steel at a joint face must be at least equal to half the negative steel at that face
The steel provided at each of the top and bottom face of the member at any section along its
length shall be at least equal to one-fourth of the maximum negative moment steel provided
at the face of either joint It may be clarified that
redistribution of moments permitted in IS 456
1978 (clause 361) will be used only for vertical
load moments and not for lateral load moments
In an external joint both the top and the bottom
bars of the beam shall be provided with anchorage
length beyond the inner face of the column equal
to the development length in tension plus 10 times
the bar diameter minus the allowance for 90 degree
bend(s) (as shown in Fig 916) In an internal joint
both face bars of the beam shall be taken
continuously through the column
Fig 916 Anchorage of Beam Bars in an External Joint (IS 13920 1993)
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9112 अनदधयय सदढीकरण की सपलाइतसोग Splicing of longitudinal reinforcement
The longitudinal bars shall be spliced only if hoops are
provided over the entire splice length at a spacing not
exceeding 150 mm (as shown in Fig 917) The lap length
shall not be less than the bar development length in tension
Lap splices shall not be provided (a) within a joint (b)
within a distance of 2d from joint face and (c) within a
quarter length of the member where flexural yielding may
generally occur under the effect of earthquake forces Not
more than 50 percent of the bars shall be spliced at one
section
Use of welded splices and mechanical connections may also be made as per 25252 of
IS 456-1978 However not more than half the reinforcement shall be spliced at a section
where flexural yielding may take place
9113 वब सदढीकरण Web Reinforcement
Web reinforcement shall consist of vertical hoops A vertical hoop is a closed stirrup having a
135deg hook with a 10 diameter extension (but
not lt 75 mm) at each end that is embedded
in the confined core [as shown in (a) of
Fig 918] In compelling circumstances it
may also be made up of two pieces of
reinforcement a U-stirrup with a 135deg hook
and a 10 diameter extension (but not lt 75
mm) at each end embedded in the confined
core and a crosstie [as shown in (b) of Fig
918] A crosstie is a bar having a 135deg hook
with a 10 diameter extension (but not lt 75
mm) at each end The hooks shall engage
peripheral longitudinal bars
912 कॉलम तजनह आर सी इमारिो ो म भको प बलो ो का तवरोध करन क तलए िाला जािा ि Columns that are required to resist Earthquake Forces in RC Buildings
Columns the vertical members in RC buildings contain two types of steel reinforcement
namely
(a) long straight bars (called longitudinal bars) placed vertically along the length and
(b) closed loops of smaller diameter steel bars (called transverse ties) placed horizontally at
regular intervals along its full length
Fig 917 Lap Splice in Beam
(IS 13920 1993)
Fig 918 Beam Web Reinforcement (IS 13920 1993)
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Columns can sustain two types of damage namely axial-flexural (or combined compression-
bending) failure and shear failure Shear damage is brittle and must be avoided in columns by
providing transverse ties at close spacing
Closely spaced horizontal closed ties (Fig 919)
help in three ways namely
(i) they carry the horizontal shear forces
induced by earthquakes and thereby resist
diagonal shear cracks
(ii) they hold together the vertical bars and
prevent them from excessively bending
outwards(in technical terms this bending
phenomenon is called buckling) and
(iii) they contain the concrete in the column
within the closed loops The ends of the
ties must be bent as 135deg hooks Such hook
ends prevent opening of loops and
consequently bulging of concrete and
buckling of vertical bars
Construction drawings with clear details of closed ties are helpful in the effective implementation
at construction site In columns where the spacing between the corner bars exceeds 300mm the
Indian Standard prescribes additional links with 180deg hook ends for ties to be effective in holding
the concrete in its place and to prevent the buckling of vertical bars These links need to go
around both vertical bars and horizontal closed ties (Fig 920) special care is required to
implement this properly at site
Designing a column involves selection of
materials to be used (ie grades of concrete and
steel bars) choosing shape and size of the cross-
section and calculating amount and distribution
of steel reinforcement The first two aspects are
part of the overall design strategy of the whole
building The IS 13920 1993 requires columns
to be at least 300mm wide A column width of up
to 200 mm is allowed if unsupported length is less
than 4m and beam length is less than 5m
Columns that are required to resist earthquake
forces must be designed to prevent shear failure
by a skillful selection of reinforcement
Fig 919 Steel reinforcement in columns ndash closed ties
at close spacing improve the performance of column
under strong earthquake shaking
Fig 920 Extra links are required to keep the
concrete in place ndash 180deg links are necessary to
prevent the135deg tie from bulging outwards
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913 एकसीयल लोिि मबसय क तलए सामानय आवशयकिाएा General Requirements for Axial
Loaded Members
These requirements apply to frame members which have a factored axial stress in excess of
01 fck under the effect of earthquake forces
The minimum dimension of the member shall not be less than 200 mm However in frames
which have beams with centre to centre span exceeding 5 m or columns of unsupported
length exceeding 4 m the shortest dimension of the column shall not be less than 300 mm
The ratio of the shortest cross sectional dimension to the perpendicular dimension shall
preferably not be less than 04
9131 अनदधयय सदढीकरण Longitudinal Reinforcement
Lap splices shall be provided only in the central half
of the member length It should be proportioned as a
tension splice Hoops shall be provided over the
entire splice length at spacing not exceeding 150
mm centre to centre Not more than 50 percent of
the bars shall be spliced at one section
Any area of a column that extends more than 100
mm beyond the confined core due to architectural
requirements shall be detailed in the following
manner
a) In case the contribution of this area to strength
has been considered then it will have the minimum longitudinal and transverse
reinforcement as per IS 13920 1993
b) However if this area has been treated as non-structural the minimum reinforcement
requirements shall be governed by IS 456 1978 provisions minimum longitudinal and
transverse reinforcement as per IS 456 1978 (as shown in Fig 921)
9132 अनपरसथ सदढीकरण Transverse Reinforcement
Transverse reinforcement for circular columns shall consist of spiral or circular hoops In
rectangular columns rectangular hoops may be used A rectangular hoop is a closed stirrup
having a 135deg hook with a 10 diameter extension (but not lt 75 mm) at each end that is
embedded in the confined core [as shown in (A) of Fig 922]
Fig 921 Reinforcement requirement for Column with more than 100 mm projection beyond core(IS 13920 1993)
Fig 922 Transverse Reinforcement in Column (IS 13920 1993)
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The parallel legs of rectangular hoop shall be spaced not more than 300 mm centre to centre
If the length of any side of the hoop exceeds 300 mm a crosstie shall be provided [as shown
in (B) of Fig 922] Alternatively a pair of overlapping hoops may be provided within the
column [as shown in (C) of Fig 922] The hooks shall engage peripheral longitudinal bars
The spacing of hoops shall not exceed half the least lateral dimension of the column except
where special confining reinforcement is provided as per Para 915 below
914 बीम-कॉलम जोड़ जो आर सी भवनो ो म भको प बलो ो का तवरोध करि ि Beam-Column Joints
that resist Earthquakes Forces in RC Buildings
In RC buildings portions of columns that are
common to beams at their intersections are
called beam column joints (Fig 923) The
joints have limited force carrying capacity
When forces larger than these are applied
during earthquakes joints are severely
damaged Repairing damaged joints is
difficult and so damage must be avoided
Thus beam-column joints must be designed
to resist earthquake effects
Under earthquake shaking the beams adjoining a joint are subjected to moments in the same
(clockwise or counter-clockwise) direction
Under these moments the top bars in the
beam-column joint are pulled in one
direction and the bottom ones in the
opposite direction These forces are
balanced by bond stress developed between
concrete and steel in the joint region
(Fig 924)
If the column is not wide enough or if the
strength of concrete in the joint is low there
is insufficient grip of concrete on the steel
bars In such circumstances the bar slips
inside the joint region and beams loose
their capacity to carry load Further under
the action of the above pull-push forces at top and bottom ends joints undergo geometric
distortion one diagonal length of the joint elongates and the other compresses
If the column cross-sectional size is insufficient the concrete in the joint develops diagonal
cracks
Fig 923 Beam-Column Joints are critical parts of a
building ndash they need to be designed
Fig924 Pull-push forces on joints cause two
problems ndash these result in irreparable damage in joints
under strong seismic shaking
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9141 बीम-कॉलम जोड़ मजबि करन क तलए सामानय आवशयकिाएा General Requirements
for Reinforcing the Beam-Column Joint
Diagonal cracking and crushing of concrete in joint
region should be prevented to ensure good
earthquake performance of RC frame buildings
(Fig 925)
Using large column sizes is the most effective
way of achieving this
In addition closely spaced closed-loop steel ties
are required around column bars to hold
together concrete in joint region and to resist
shear forces
Intermediate column bars also are effective in
confining the joint concrete and resisting
horizontal shear forces Providing closed-loop
ties in the joint requires some extra effort
IS 13920ndash1993 recommends continuing the
transverse loops around the column bars
through the joint region
In practice this is achieved by preparing the cage of
the reinforcement (both longitudinal bars and
stirrups) of all beams at a floor level to be prepared
on top of the beam formwork of that level and
lowered into the cage (Fig 926)
However this may not always be possible
particularly when the beams are long and the entire
reinforcement cage becomes heavy
The gripping of beam bars in the joint region is
improved first by using columns of reasonably
large cross-sectional size
The Indian Standard IS 13920-1993 requires building columns in seismic zones III IV and V to
be at least 300mm wide in each direction of the cross-section when they support beams that are
longer than 5m or when these columns are taller than 4m between floors (or beams)
In exterior joints where beams terminate at columns longitudinal beam bars need to be anchored
into the column to ensure proper gripping of bar in joint The length of anchorage for a bar of
grade Fe415 (characteristic tensile strength of 415MPa) is about 50 times its diameter This
Fig 925 Closed loop steel ties in beam-column
joints ndash such ties with 135deg hooks resist the ill
effects of distortion of joints
Fig 926 Providing horizontal ties in the joints ndash
three-stage procedure is required
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length is measured from the face of the column to the end of the bar anchored in the column
(Fig 927)
In columns of small widths and when beam
bars are of large diameter (Fig 928(a)) a
portion of beam top bar is embedded in the
column that is cast up to the soffit of the
beam and a part of it overhangs It is difficult
to hold such an overhanging beam top bar in
position while casting the column up to the
soffit of the beam Moreover the vertical
distance beyond the 90ordm bend in beam bars is
not very effective in providing anchorage
On the other hand if column width is large
beam bars may not extend below soffit of the
beam (Fig 928 (b)) Thus it is preferable to
have columns with sufficient width
In interior joints the beam bars (both top and
bottom) need to go through the joint without
any cut in the joint region Also these bars
must be placed within the column bars and
with no bends
915 तवशष सीतमि सदढीकरण Special Confining Reinforcement
This requirement shall be met with unless a
larger amount of transverse reinforcement is
required from shear strength considerations
Special confining reinforcement shall be
provided over a length lsquolorsquo from each
joint face towards mid span and on
either side of any section where flexural
yielding may occur under the effect of
earthquake forces (as shown in Fig 929)
The length lsquolorsquo shall not be less than
(a) larger lateral dimension of the
member at the section where yielding
occurs
(b) 16 of clear span of the member and
(c) 450 mm
Fig 929 Column and Joint Detailing (IS 13920 1993)
Fig 927 Anchorage of beam bars in exterior
joints ndash diagrams show elevation of joint region
Fig 928 Anchorage of beam bars in interior
jointsndash diagrams (a) and (b) show cross-sectional
views in plan of joint region
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When a column terminates into a footing or mat special confining reinforcement shall extend
at least 300 mm into the footing or mat (as shown in Fig 930)
When the calculated point of contra-flexure
under the effect of gravity and earthquake
loads is not within the middle half of the
member clear height special confining
reinforcement shall be provided over the full
height of the column
Columns supporting reactions from discontinued stiff members such as walls shall be
provided with special confining reinforcement over their full height (as shown in Fig 931)
This reinforcement shall also be placed above the discontinuity for at least the development
length of the largest longitudinal bar in the column Where the column is supported on a wall
this reinforcement shall be provided
over the full height of the column it
shall also be provided below the
discontinuity for the same development
length
Special confining reinforcement shall
be provided over the full height of a
column which has significant variation
in stiffness along its height This
variation in stiffness may result due to
the presence of bracing a mezzanine
floor or a RCC wall on either side of
the column that extends only over a part
of the column height (as shown in Fig
931)
916 तवशषिः भको पीय कषतर म किरनी दीवारो ो वाली इमारिो ो का तनमायण Construction of Buildings
with Shear Walls preferably in Seismic Regions
Reinforced concrete (RC) buildings often have vertical
plate-like RC walls called Shear Walls in addition to
slabs beams and columns These walls generally start
at foundation level and are continuous throughout the
building height Their thickness can be as low as
150mm or as high as 400mm in high rise buildings
Shear walls are usually provided along both length and
width of buildings Shear walls are like vertically-
oriented wide beams that carry earthquake loads
downwards to the foundation (Fig 932)
Fig 932 Reinforced concrete shear walls in
buildings ndash an excellent structural system for
earthquake resistance
Fig 930 Provision of Special confining reinforcement in Footings (IS 13920 1993)
Fig 931 Special Confining Reinforcement Requirement for
Columns under Discontinued Walls (IS 13920 1993)
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Properly designed and detailed buildings with shear walls have shown very good performance in
past earthquakes Shear walls in high seismic regions require special detailing Shear walls are
efficient both in terms of construction cost and effectiveness in minimizing earthquake damage
in structural and non-structural elements (like glass windows and building contents)
Shear walls provide large strength and
stiffness to buildings in the direction of their
orientation which significantly reduces lateral
sway of the building and thereby reduces
damage to structure and its contents
Since shear walls carry large horizontal
earthquake forces the overturning effects on
them are large Thus design of their
foundations requires special attention
Shear walls should be provided along
preferably both length and width However if
they are provided along only one direction a
proper grid of beams and columns in the
vertical plane (called a moment-resistant
frame) must be provided along the other
direction to resist strong earthquake effects
Door or window openings can be provided in shear walls but their size must be small to
ensure least interruption to force flow through walls
Shear walls in buildings must be symmetrically located in plan to reduce ill-effects of twist in
buildings (Fig 933)
Shear walls are more effective when located along exterior perimeter of the building ndash such a
layout increases resistance of the building to twisting
9161 िनय तिजाइन और किरनी दीवारो ो की जयातमति Ductile Design and Geometry of Shear
Walls
Shear walls are oblong in cross-section ie one dimension of the cross-section is much larger
than the other While rectangular cross-section is common L- and U-shaped sections are also
used Overall geometric proportions of the wall types and amount of reinforcement and
connection with remaining elements in the building help in improving the ductility of walls The
Indian Standard Ductile Detailing Code for RC members (IS13920-1993) provides special
design guidelines for ductile detailing of shear walls
917 इमपरवड़ तिजाइन रणनीतियाो Improved design strategies
9171 िातनकारक भको प परभाव स भवनो ो का सोरकषण Protection of Buildings from Damaging
Earthquake Effects
Conventional seismic design attempts to make buildings that do not collapse under strong
earthquake shaking but may sustain damage to non-structural elements (like glass facades) and
to some structural members in the building There are two basic technologies ndashBase Isolation
Fig 933 Shear walls must be symmetric in plan
layout ndash twist in buildings can be avoided
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Devices and Seismic Dampers which are used to protect buildings from damaging earthquake
effects
9172 आधार अलगाव Base Isolation
The idea behind base isolation is to detach (isolate) the building from the ground in such a way
that earthquake motions are not transmitted up through the building or at least greatly reduced
As illustrated in Fig 934 when the ground shakes the rollers freely roll but the building
above does not move Thus no force is
transferred to the building due to shaking of
the ground simply the building does not
experience the earthquake
As illustrated in Fig 935 if the same
building is rested on flexible pads that offer
resistance against lateral movements then
some effect of the ground shaking will be
transferred to the building above
As illustrated in Fig 936 if the flexible
pads are properly chosen the forces induced
by ground shaking can be a few times
smaller than that experienced by the
building built directly on ground namely a
fixed base building
9173 भको पी सोज Seismic Dampers
Seismic dampers are special devices introduced in the building to absorb the energy provided by
the ground motion to the building These dampers act like the hydraulic shock absorbers in cars ndash
much of the sudden jerks are absorbed in the hydraulic fluids and only little is transmitted above
to the chassis of the car
When seismic energy is transmitted through them dampers absorb part of it and thus damp the
motion of the building Commonly used types of seismic dampers (Fig 937) include
Fig 934 Hypothetical Building
Fig 935 Base Isolated Building
Fig 936 Fixed-Base Building
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Viscous dampers ndash Energy is absorbed by
silicone-based fluid passing between piston-
cylinder arrangement
Friction dampers ndash Energy is absorbed by
surfaces with friction between them rubbing
against each other
Yielding dampers ndash Energy is absorbed by
metallic components that yield
In India friction dampers have been provided in an
18-storey RC frame structure in Gurgaon
918 तिजाइन उदािरण Design Example ndash Beam Design of RC Frame with Ductile
Detailing
Exercise ndash 2 Beam Design of RC Frame Building as per Provision of IS 13920 1993 and IS
1893 (Part 1) 2002 Beam marked ABC is considered for Design
Fig 937 Seismic Energy Dissipation Devices
each device is suitable for a certain building
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ELEVATION
Solution
1 General Data Grade of Concrete = M 25
Grade of steel = Fe 415 Tor Steel
2 Load Combinations
As per Cl 63 of IS 1893 (Part 1) 2002 following are load combinations for Earthquake
Loading
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S No Load Combination DL LL EQ Remark
1 15 DL + 15 LL 15 15 ndash As per Table ndash 8
of IS 1893 (Part
1) 2002 2 12 (DL + LL
+ EQx) 15 025 or 050 +12
3 12 (DL + LL ndash EQx) 15 025 or 050 ndash12
4 12 (DL + LL + EQy) 15 025 or 050 +12
5 12 (DL + LL ndash EQy) 15 025 or 050 ndash12
6 15 (DL + EQx) 15 +15
7 15 (DL ndash EQx) 15 ndash15
8 15 (DL + EQy) 15 +15
9 15 (DL ndash EQy) 15 ndash15
10 09 DL + 15 EQx 15 +15
11 09 DL ndash 15 EQx 15 ndash15
12 09 DL + 15 EQy 15 +15
13 09 DL ndash 15 EQy 15 ndash15
EQx implies EQ Loading in X ndash direction amp EQy implies EQ Loading in Y ndash direction
where X amp Y are orthogonal directions and Z is vertical direction These load combinations
are for EQ Loading In practice Wind Load should also be considered in lieu of EQ Load
and critical of the two should be used in the design
In this exercise emphasis is to show calculations for ductile design amp detailing of building
elements subjected to Earthquake in the plan considered Beams parallel to Y ndash direction are
not significantly affected by Earthquake force in X ndash direction (except in case of highly
unsymmetrical building) and vice versa Beams parallel to Y ndash direction are designed for
Earthquake loading in Y ndash direction only
Torsion effect is not considered in this example
3 Force Data
For Beam AB force resultants for various load cases (ie DL LL amp EQ Load) from
Computer Analysis (or manually by any method of analysis) to illustrate the procedure of
design are tabulated below
Table ndash A Force resultants in beam AB for various load cases
Load Case Left End Centre Right End
Shear
(KN)
Moment
(KN-m)
Shear
(KN)
Moment
(KN-m)
Shear
(KN)
Moment
(KN-m)
DL ndash 51 ndash 37 4 32 59 ndash 56
LL ndash 14 ndash 12 1 11 16 ndash 16
EQY 79 209 79 11 79 ndash 119
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Table ndash B Force resultants in beam AB for different load combinations
Load Combinations Left End Centre Right End
Shear
(KN)
Moment
(KN-m)
Shear
(KN)
Moment
(KN-m)
Shear
(KN)
Moment
(KN-m)
15 DL + 15 LL 98 ndash 74 7 64 111 ndash 108
12 (DL + LL + EQy) 31 205 101 52 172 ndash 303
12 (DL + LL ndash EQy) 162 ndash 300 92 31 22 159
15 (DL + EQy) 44 261 127 61 209 ndash 372
15 (DL ndash EQy) 97 ndash 371 115 34 33 205
09 DL + 15 EQy 75 283 124 42 174 ndash 339
09 DL ndash 15 EQy 167 ndash 349 117 15 68 238
4 Various checks for Flexure Member
(i) Check for Axial Stress
As per Cl 611 of IS 13920 1993 flexural axial stress on the member under EQ loading
shall not exceed 01 fck
Factored Axial Force = 000 KN
Factored Axial Stress = 000 MPa lt 010 fck OK
Hence the member is to be designed as Flexure Member
(ii) Check for Member size
As per Cl 613 of IS 13920 1993 width of the member shall not be less than 200 mm
Width of the Beam B = 250 mm gt 200 mm OK
Depth of Beam D = 550 mm
As per Cl 612 member shall have a width to depth ratio of more than 03
BD = 250550 = 04545 gt 03 OK
As per Cl 614 depth of member shall preferably be not more than 14 of the clear span
ie (DL) lt 14 or (LD) gt4
Span = 4 m LD = 4000550 = 727 gt 4 OK
Check for Limiting Longitudinal Reinforcement
Nominal cover to meet Durability requirements as per = 30 mm
Table ndash 16 of IS 4562000 (Cl 2642) for Moderate Exposure
Effective depth for Moderate Exposure conditions = 550 ndash 30 ndash 20 ndash (202)
with 20 mm of bars in two layers = 490 mm
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As per Cl 621 (b) of IS 13920 1993 tension steel ratio on any face at any section shall not
be less than = (024 radic fck) fy
= (024 radic25) 415 = 0289 asymp 029
Min Reinforcement = (029100) X 250 X 490 = 356 mm2
Max Reinforcement 25 = (25100) X 250 X 490 = 3063 mm2
(iii) Design for Flexure
Design for Hogging Moment at support A
At end A from Table ndash B Mu = 371 KN-m
Therefore Mu bd2 = 371x10
6 (250 x 490 x 490) = 618
Referring to Table ndash 51 of SP ndash 16 for drsquod = 55490 = 011
We get Ast at top = 2013 Asc = 0866
Therefore Ast at top = (2013100) x 250 x 490
= 2466 mm2
gt 356 mm2 (Min Reinforcement)
lt 3063 mm2 (Max Reinforcement)
Asc at bottom = 0866
As per Cl 623 of IS 13290 1993 positive steel at a joint face must be at least equal to half
the ndashve steel at that face Therefore Asc at bottom must be at least 50 of Ast hence
Revised Asc = 20132 = 10065
Asc at bottom = (10065100) x 250 x 490
= 1233 mm2 gt 426 mm
2 (Min Reinforcement)
lt 3063 mm2 (Max Reinforcement)
Design for Sagging Moment at support A
Mu = 283 KN-m
The beam will be designed as T-beam The limiting capacity of the T-beam assuming xu lt Df
and xu lt xumax may be calculated as follows
Mu = 087 fy Ast d [1- (Ast fy bf d fck)] -------- (Eq ndash 1)
Where Df = Depth of Flange
= 150 mm
xu = Depth of Neutral Axis
xumax = Limiting value of Neutral Axis
= 048 d
= 048 X 490
= 23520 mm
bw = 250 mm
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83
bf = Width of Flange
= (L06) + bw + 6 Df or cc of beam
= (07 X 40006) + 250 + 6 X 150
= 467 + 250 + 900 = 1617 mm or 4000 mm cc
[Lower of two is to be adopted]
Substituting the values in Eq ndash 1 and solving the quadratic equation
283 X 106 = 087 X 415 Ast X 490 [1ndash (Ast X 415) (1617 X 490 X 25)]
= 1769145 Ast [1 ndash 2095 X 10-5
Ast]
283 X 106 = 1769145 Ast ndash 3706 Ast
2]
3706 Ast2 ndash 1769145 Ast + 283 X 10
6 = 0
Ast = [1769145 plusmn radic(17691452 ndash 4 X 3706 X 283 X 10
6)] 2 X 3706
= [1769145 plusmn radic(3129874 X 1010
ndash 4195192 X 106)] 2 X 3706
= (1769145 plusmn 16463155) 7412
Ast at bottom = 165717 mm2 gt 35600 mm
2
lt 306300 mm2 OK
It is necessary to check the design assumptions before finalizing the reinforcement
xu = (087 fy Ast) (036 fck bf)
= (087 X 415 X 1657) (036 X 25 X 1617)
= 4110 mm lt 150 mm OK
lt df
lt xumax = 048 X 490 = 235 mm OK
Ast = [1657(250X490)] X 100 = 1353
As per Cl 624 ldquoSteel provided at each of the top amp bottom face of the member at any one
section along its length shall be at least equal to 14th
of the maximum (-ve) moment steel
provided at the face of either joint
For Centre Mu = 64 KN-m
64 X 106 = 087 X 415 Ast X 490 [1ndash (Ast X 415) (1617 X 490 X 25)]
= 1769145 Ast [1 ndash 2095 X 10-5
Ast]
64 X 106 = 1769145 Ast ndash 3706 Ast
2]
3706 Ast2 ndash 1769145 Ast + 64 X 10
6 = 0
Ast = [1769145 plusmn radic(17691452 ndash 4 X 3706 X 64 X 10
6)] 2 X 3706
= 365 mm2
For Right Support Mu = 238 KN-m
238 X 106 = 087 X 415 Ast X 490 [1ndash (Ast X 415) (1617 X 490 X 25)]
= 1769145 Ast [1 ndash 2095 X 10-5
Ast]
238 X 106 = 1769145 Ast ndash 3706 Ast
2]
3706 Ast2 ndash 1769145 Ast + 238 X 10
6 = 0
Ast = [1769145 plusmn radic(17691452 ndash 4 X 3706 X 238 X 10
6)] 2 X 3706
= 1386 mm2
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(iv) Reinforcement Requirement
Top reinforcement is larger of Ast at top for hogging moment or Asc at top for sagging
moment ie 2466 mm2 or 968 mm
2 Hence provide 2466 mm
2 at top
Bottom reinforcement is larger of Asc at bottom for hogging moment or Ast at bottom for
sagging moment ie 1233 mm2 or 1936 mm
2 Hence provide 1936 mm
2 at bottom
Details of Reinforcement
Top Reinforcement
Beam AB Left End Centre Right End
Hogging Moment ndash 371 - ndash 371
Mu bd2 618 - 618
Ast at top 2013 - 2013
Asc at bottom 0866 lt 2013 2 =
10065 Hence
revised Asc = 10065
- 0866
Revised to
10065 as per Cl
623 of IS
139201993
Bottom Reinforcement
Sagging Moment 283 64 238
Ast at bottom Ast req = 1657 mm2
= 1353
gt 20132 =
10065 OK
Provide Ast at bottom
= 1353
Ast req = 365 mm2
= 0298
gt 029
gt 20134 =
0504 OK
As per Cl 624 of IS
139201993
Provide Ast at bottom
= 0504
Ast req = 1386 mm2
= 117
gt 029
gt 20132 =
10065
Provide Ast at
bottom = 117
Asc at top Asc req = 1657 2
= 829 mm2
= 0677
gt 029
gt 2013 4 =
0504 OK
Asc req = 05042
= 0252
gt 029 Provide MinAsc = 029
Asc req = 1657 2
= 829 mm2
= 0677
gt 029
gt 2013 4
= 0504
OK
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Summary of Reinforcement required
Beam Left End Centre Right End
Top = 2013
= 2466 mm2
Bottom = 1353
= 1658 mm2
Top = 0504
= 618 mm2
Bottom = 0504
= 618 mm2
Top = 2013
= 2466 mm2
Bottom = 10065
= 1233 mm2
Reinforcement provided
2 ndash 20Φ cont + 4 ndash 25Φ extra
Ast = 2592 mm2 (2116)
2 ndash 20Φ cont + 2 ndash 20Φ extra
+ 2 ndash 16 Φ
Ast = 1658 mm2 (1353)
2 ndash 20Φ cont
Ast = 628 mm2 (0512)
2 ndash 20Φ cont
Ast = 628 mm2 (0512)
2 ndash 20Φ cont
+ 4 ndash 25Φ extra
Top = 2592 mm2
2 ndash 20Φ cont
+ 2 ndash 20Φ extra + 2 ndash 16Φ
Ast = 1658 mm2 (1353)
Details of Reinforcement
Ld = Development Length in tension
db = Dia of bar
For Fe 415 steel and M25 grade concrete as per Table ndash 65 of SP ndash 16
For 25Φ bars 1007 + 10Φ - 8Φ = 1007+50 = 1057 mm
For 20Φ bars 806 + 2Φ = 806+40 = 846 mm
(v) Design for Shear
Tensile steel provided at Left End = 2116
Permissible Design Stress of Concrete
(As per Table ndash 19 of IS 4562000) τc = 0835 MPa
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86
Design Shear Strength of Concrete = τc b d
= (0835 X 250 X 490) 1000
= 102 KN
Similarly Design Shear Strength of Concrete at centre for Ast = 0512
τc = 0493 MPa
Shear Strength of Concrete at centre = τc b d
= (0493 X 250 X 490) 1000
= 6040 KN
(vi) Shear force due to Plastic Hinge Formation at the ends of the beam
The additional shear due to formation of plastic hinges at both ends of the beams is evaluated
as per Cl 633 of IS 139201993 is given by
Vsway to right = plusmn 14 [MulimAs
+ MulimBh
] L
Vsway to left = plusmn 14 [MulimAh
+ MulimBs
] L
Where
MulimAs
= Sagging Ultimate Moment of Resistance of Beam Section at End A
MulimAh
= Hogging Ultimate Moment of Resistance of Beam Section at End A
MulimBh
= Sagging Ultimate Moment of Resistance of Beam Section at End B
MulimBs
= Hogging Ultimate Moment of Resistance of Beam Section at End B
At Ends beam is provided with steel ndash pt = 2116 pc = 1058
Referring Table 51 of SP ndash 16 for pt = 2116 pc = 1058
The lowest value of MuAh
bd2 is found
MuAh
bd2 = 645
Hogging Moment Capacity at End A
MuAh
= 645 X 250 X 4902
= 38716 X 108 N-mm
= 38716 KN-m
Similarly for MuAs
pt = 1058 pc = 2116
Contribution of Compressive steel is ignored while calculating the Sagging Moment
Capacity at T-beam
MuAs
= 087 fy Ast d [1- (Ast fy bf d fck)]
= 087 X 415 X 1658 X 490 [1ndash (1658 X 415 1617 X 490 X 25)]
= 28313 KN-m
Similarly for Right End of beam
MuBh
= 38716 KN-m amp MuBs
= 28313 KN-m
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Shear due to Plastic Hinge is calculated as
Vsway to right = plusmn 14 [MuAs
+ MuBh
] L
= plusmn 14 [28313 + 38716] 4
= 23460 KN
Vsway to left = plusmn 14 [MuAh
+ MuBs
] L
= plusmn 14 [38716 + 28313] 4
= 23460 KN
Design Shear
Dead Load of Slab = 50 KNm2 Live Load = 40 KNm
2
Load due to Slab in Beam AB = 2 X [12 X 4 X 2] X 5 = 40 KN (10 KNm)
Self Wt Of Beam = 025 X 055 X 25 X 4 = 1375 KN (344 KNm)
asymp 1400 KN
Live Load = 2 X [12 X 4 X 2] X 4 = 32 KN (8 KNm)
Shear Force due to DL = 12 X [40 + 14] = 27 KN
Shear Force due to LL = 12 X [32] = 16 KN
As per Cl 633 of IS 139201993 the Design shear at End A ie Vua and Design Shear at
End B ie Vub are computed as
(i) For Sway Right
Vua = VaD+L
ndash 14 [MulimAs
+ MulimBh
] LAB
Vub = VbD+L
+ 14 [MulimAs
+ MulimBh
] LAB
(ii) For Sway Left
Vua = VaD+L
+ 14 [MulimAh
+ MulimBs
] LAB
Vub = VbD+L
ndash 14 [MulimAh
+ MulimBs
] LAB
Where
VaD+L
amp VbD+L
= Shear at ends A amp B respectively due to vertical load with
Partial Safety Factor of 12 on Loads
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VaD+L
= VbD+L
= 12 (D+L) 2
--------------For equ (i)
---------------For equ (ii)
14 X [MuAs
+ MuBh
] L = 23460 KN
14 X [MuAh
+ MuBs
] L = 23460 KN
VaD = Vb
D = 12 X 27 = 324
= 516
VaL = Vb
L = 12 X 16 = 192
Vua = [12 (27+16)] ndash 23460 = 516 ndash 23460 = (-) 18300 KN
Vub = [12 (27+16)] + 23460 = 516 + 23460 = (+) 28620 KN
Vub = [12 (27+16)] + 23460 = 516 + 23460 = (+) 28620 KN
Vua = [12 (27+16)] ndash 23460 = 516 ndash 23460 = (-) 18300 KN
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As per Cl 633 of IS 139201993 the Design Shear Force to be resisted shall be of
maximum of
(i) Calculate factored SF as per analysis ( Refer Table ndash B)
(ii) Shear Force due to formation of Plastic Hinges at both ends of the beam plus
factored gravity load on the span
Hence Design shear Force Vu will be 28620 KN (corresponding to formation of Plastic
Hinge)
From Analysis as per Table ndash B SF at mid-span of the beam is 127 KN However Shear
due to formation of Plastic Hinge is 23460 KN Hence design shear at centre of span is
taken as 23460 KN
The required capacity of shear reinforcement at ends
Vus = Vu - Vc
= 28620 ndash 102
= 18420 KN
And at centre Vus = 23460 ndash 6040
= 17420 KN
At supports
Vus d = 28620 49 = 584 KNcm
Therefore requirement of stirrups is
12Φ ndash 2 legged strippus 135 cc [Vus d = 606]
However provide 12Φ ndash 2 legged strippus 120 cc as per provision of Cl 635 of IS
139201993 [Vus d = 6806]
At centre
Vus d = 23460 49 = 478 KNcm
Provide 12Φ ndash 2 legged strippus 170 cc [Vus d = 4804]
As per Cl 635 of IS 139201993 the spacing of stirrups in the mid-span should not
exceed d2 = 4902 = 245 mm
Minimum Shear Reinforcement as per Cl 26516 of IS 4562000 is
Sv = Asv X 08 fy 046
= (2 X 79 X 087 X 415) (250 X 04)
= 570 mm
As per CL 635 of IS 139201993 ldquoSpacing of Links over a length of 2d at either end of
beam shall not exceed
(i) d4 = 4904 = 12250 mm
(ii) 8 times dia of smallest longitudinal bar = 8 X 16 = 128 mm
However it need not be less than 100 mm
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The reinforcement detailing is shown as below
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अधयाय Chapter ndash 10
अलप सामरथय तचनाई सोरचनाओो क तनमायण Construction of Low Strength Masonry Structures
Two types of construction are included herein namely
a) Brick construction using weak mortar and
b) Random rubble and half-dressed stone masonry construction using different mortars such as
clay mud lime-sand and cement sand
101 भको प क दौरान ईोट तचनाई की दीवारो ो का वयविार Behaviour of Brick Masonry Walls
during Earthquakes
Of the three components of a masonry building (roof wall and foundation as illustrated in
Fig101) the walls are most vulnerable to damage caused by horizontal forces due to earthquake
Ground vibrations during earthquakes cause inertia forces at locations of mass in the building (Fig 102) These forces travel through the roof and walls to the foundation The main emphasis
is on ensuring that these forces reach the ground without causing major damage or collapse
A wall topples down easily if pushed
horizontally at the top in a direction
perpendicular to its plane (termed weak
Fig 101 Basic components of Masonry Building
Fig 103 For the direction of Earthquake shaking
shown wall B tends to fail
at its base
Fig 102 Effect of Inertia in a building when shaken
at its base
Fig 104 Direction of force on a wall critically determines
its earthquake performance
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direction) but offers much greater resistance if pushed along its length (termed strong direction) (Fig 103 amp 104)
The ground shakes simultaneously in the vertical and two horizontal directions during
earthquakes However the horizontal vibrations are the most damaging to normal masonry
buildings Horizontal inertia force developed at the
roof transfers to the walls acting either in the weak
or in the strong direction If all the walls are not tied
together like a box the walls loaded in their weak
direction tend to topple
To ensure good seismic performance all walls must
be joined properly to the adjacent walls In this way
walls loaded in their weak direction can take
advantage of the good lateral resistance offered by
walls loaded in their strong direction (Fig 105)
Further walls also need to be tied to the roof and
foundation to preserve their overall integrity
102 तचनाई वाली इमारिो ो म बॉकस एकशन कस सतनतिि कर How to ensure Box Action in
Masonry Buildings
A simple way of making these walls behave well during earthquake shaking is by making them
act together as a box along with the roof at the top and with the foundation at the bottom A
number of construction aspects are required to ensure this box action
Firstly connections between the walls should be good This can be achieved by (a) ensuring
good interlocking of the masonry courses at the junctions and (b) employing horizontal bands
at various levels particularly at the lintel level
Secondly the sizes of door and window
openings need to be kept small The smaller
the opening the larger is the resistance
offered by the wall
Thirdly the tendency of a wall to topple
when pushed in the weak direction can be
reduced by limiting its length-to-thickness
and height to-thickness ratios Design codes
specify limits for these ratios A wall that is
too tall or too long in comparison to its
thickness is particularly vulnerable to
shaking in its weak direction (Fig 106)
Fig 106 Slender walls are vulnerable
Fig 105 Wall B properly connected to Wall A
(Note roof is not shown) Walls A
(loaded in strong direction) support
Walls B (loaded in weak direction)
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Brick masonry buildings have large mass and hence attract large horizontal forces during
earthquake shaking They develop numerous cracks under both compressive and tensile forces
caused by earthquake shaking The focus of earthquake resistant masonry building construction
is to ensure that these effects are sustained without major damage or collapse Appropriate choice
of structural configuration can help achieve this
The structural configuration of masonry buildings
includes aspects like (a) overall shape and size of the
building and (b) distribution of mass and
(horizontal) lateral load resisting elements across the
building
Large tall long and un-symmetric buildings perform
poorly during earthquakes A strategy used in making
them earthquake resistant is developing good box
action between all the elements of the building ie
between roof walls and foundation (Fig 107) For
example a horizontal band introduced at the lintel
level ties the walls together and helps to make them
behave as a single unit
103 कषतिज बि की भतमका Role of Horizontal Bands
Horizontal bands are the most important
earthquake-resistant feature in masonry
buildings The bands are provided to hold a
masonry building as a single unit by tying all
the walls together and are similar to a closed
belt provided around cardboard boxes
(Fig 108 amp 109)
The lintel band undergoes bending and pulling actions during earthquake shaking
(Fig1010)
To resist these actions the construction of lintel band requires special attention
Fig 107 Essential requirements to ensure
box action in a masonry building
Fig 108 Building with flat roof
Fig 109 Two-storey Building with pitched roof
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Bands can be made of wood (including bamboo splits) or of reinforced concrete (RC) the
RC bands are the best (Fig 1011)
The straight lengths of the band must be properly connected at the wall corners
In wooden bands proper nailing of straight lengths with spacers is important
In RC bands adequate anchoring of steel links with steel bars is necessary
The lintel band is the most important of all and needs to be provided in almost all buildings
The gable band is employed only in buildings with pitched or sloped roofs
In buildings with flat reinforced concrete or reinforced brick roofs the roof band is not
required because the roof slab also plays the role of a band However in buildings with flat
timber or CGI sheet roof roof band needs to be provided In buildings with pitched or sloped
roof the roof band is very important
Plinth bands are primarily used when there is concern about uneven settlement of foundation
soil
Lintel band Lintel band is a band provided at lintel level on all load bearing internal external
longitudinal and cross walls
Roof band Roof band is a band provided immediately below the roof or floors Such a band
need not be provided underneath reinforced concrete or brick-work slabs resting on bearing
Fig 1010 Bending and pulling in lintel bands ndash Bands must be capable of resisting these actions
Fig 1011 Horizontal Bands in masonry buildings ndash RC bands are the best
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walls provided that the slabs are continuous over the intermediate wall up to the crumple
sections if any and cover the width of end walls fully or at least 34 of the wall thickness
Gable band Gable band is a band provided at the top of gable masonry below the purlins This
band shall be made continuous with the roof band at the eaves level
Plinth band Plinth band is a band provided at plinth level of walls on top of the foundation
wall This is to be provided where strip footings of masonry (other than reinforced concrete or
reinforced masonry) are used and the soil is either soft or uneven in its properties as frequently
happens in hill tracts This band will serve as damp proof course as well
104 अधोलोब सदढीकरण Vertical Reinforcement
Vertical steel at corners and junctions of walls which are up to 340 mm (1frac12 brick) thick shall be
provided as specified in Table 101 For walls thicker than 340 mm the area of the bars shall be
proportionately increased
No vertical steel need be provided in category A building The vertical reinforcement shall be
properly embedded in the plinth masonry of foundations and roof slab or roof band so as to
develop its tensile strength in bond It shall be passing through the lintel bands and floor slabs or
floor level bands in all storeys
Table ndash 101 Vertical Steel Reinforcement in Masonry Walls with Rectangular Masonry Units (IS 4326 1993)
No of Storeys Storey Diameter of HSD Single Bar in mm at Each Critical Section
Category B Category C Category D Category E One mdash Nil Nil 10 12
Two Top
Bottom
Nil
Nil
Nil
Nil
10
12
12
16
Three Top
Middle
Bottom
Nil
Nil
Nil
10
10
12
10
12
12
12
16
16
Four Top
Third
Second
Bottom
10
10
10
12
10
10
12
12
10
12
16
20
Four storeyed
building not
permitted
NOTES
1 The diameters given above are for HSD bars For mild-steel plain bars use equivalent diameters as given under
Table ndash 106 Note 2
2 The vertical bars will be covered with concrete M15 or mortar 1 3 grade in suitably created pockets around the
bars This will ensure their safety from corrosion and good bond with masonry
3 In case of floorsroofs with small precast components also refer 923 of IS 4326 1993 for floorroof band details
Bars in different storeys may be welded (IS 2751 1979 and IS 9417 1989 as relevant) or
suitably lapped
Vertical reinforcement at jambs of window and door openings shall be provided as per
Table ndash 101 It may start from foundation of floor and terminate in lintel band (Fig 1017)
Typical details of providing vertical steel in brickwork masonry with rectangular solid units
at corners and T-junctions are shown in Fig 1012
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105 दीवारो ो म सराखो ो का सोरकषण Protection of Openings in Walls
Horizontal bands including plinth band lintel band and roof band are provided in masonry
buildings to improve their earthquake performance Even if horizontal bands are provided
masonry buildings are weakened by the openings in their walls
Embedding vertical reinforcement bars in the edges of the wall piers and anchoring them in the
foundation at the bottom and in the roof band at the top forces the slender masonry piers to
undergo bending instead of rocking In wider wall piers the vertical bars enhance their capability
to resist horizontal earthquake forces and delay the X-cracking Adequate cross-sectional area of
these vertical bars prevents the bar from yielding in tension Further the vertical bars also help
protect the wall from sliding as well as from collapsing in the weak direction
However the most common damage observed after an earthquake is diagonal X-cracking of
wall piers and also inclined cracks at the corners of door and window openings
When a wall with an opening deforms during earthquake shaking the shape of the opening
distorts and becomes more like a rhombus - two opposite corners move away and the other two
come closer Under this type of deformation the corners that come closer develop cracks The
cracks are bigger when the opening sizes are larger Steel bars provided in the wall masonry all
Fig 1012 Typical Details of Providing Vertical Steel Bars in Brick Masonry (IS 4326 1993)
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around the openings restrict these cracks at the corners In summary lintel and sill bands above
and below openings and vertical reinforcement adjacent to vertical edges provide protection
against this type of damage (Fig 1013)
106 भको प परतिरोधी ईोट तचनाई भवन क तनमायण िि सामानय तसदाोि General Principles for
Construction of Earthquake Resistant Brick Masonry Building
Low Strength Masonry constructions should not be permitted for important buildings
It will be useful to provide damp-proof course at plinth level to stop the rise of pore water
into the superstructure
Precautions should be taken to keep the rain water away from soaking into the wall so that
the mortar is not softened due to wetness An effective way is to take out roof projections
beyond the walls by about 500 mm
Use of a water-proof plaster on outside face of walls will enhance the life of the building and
maintain its strength at the time of earthquake as well
Ignoring tensile strength free standing walls should be checked against overturning under the
action of design seismic coefficient ah allowing for a factor of safety of 15
1061 भवनो ो की शरतणयाा Categories of Buildings
For the purpose of specifying the earthquake resistant features in masonry and wooden buildings
the buildings have been categorized in five categories A to E based on the seismic zone and the
importance of building I
Where
I = importance factor applicable to the
building [Ref Clause 642 and
Table - 6 of IS 1893 (Part 1) 2002]
The building categories are given in
Table ndash 102
Fig 1013 Cracks at corners of openings in a masonry building ndash reinforcement around them helps
Table -102 Building Categories for Earthquake Resisting Features (IS 4326 1993)
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98
1062 कमजोर गार म ईोट तचनाई कायय Brickwork in Weak Mortars
The fired bricks should have a compressive strength not less than 35 MPa Strength of bricks
and wall thickness should he selected for the total building height
The mortar should be lime-sand (13) or clay mud of good quality Where horizontal steel is
used between courses cement-sand mortar (13) should be used with thickness so as to cover
the steel with 6 mm mortar above and below it Where vertical steel is used the surrounding
brickwork of 1 X 1 or lfrac12 X 1frac12 brick size depending on wall thickness should preferably be
built using 16 cement-sand mortar
The minimum wall thickness shall be one brick in one storey construction and one brick in
top storey and 1frac12brick in bottom storeys of up to three storey constructions It should also
not be less than l16 of the length of wall between two consecutive perpendicular walls
The height of the building shall be restricted to the following where each storey height shall
not exceed 30 m
For Categories A B and C - three storeys with flat roof and two storeys plus attic pitched
roof
For Category D - two storeys with flat roof and one storey plus attic for pitched roof
1063 आयिाकार तचनाई इकाइयो ो वाला तचनाई तनमायण Masonry Construction with
Rectangular Masonry Units
General requirements for construction of masonry walls using rectangular masonry units are
10631 तचनाई इकाइयाो Masonry Units
Well burnt bricks conforming to IS 1077 1992 or solid concrete blocks conforming to IS
2185 (Part 1) 1979 and having a crushing strength not less than 35 MPa shall be used The
strength of masonry unit required
shall depend on the number of storeys
and thickness of walls
Squared stone masonry stone block
masonry or hollow concrete block
masonry as specified in IS 1597 (Part
2) 1992 of adequate strength may
also be used
10632 गारा Mortar
Mortars such as those given in Table
ndash 103 or of equivalent specification
shall preferably be used for masonry
Table ndash 103 Recommended Mortar Mixes (IS 4326 1993)
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construction for various categories of buildings
Where steel reinforcing bars are provided in masonry the bars shall be embedded with
adequate cover in cement sand mortar not leaner than 13 (minimum clear cover 10 mm) or in
cement concrete of grade M15 (minimum clear cover 15 mm or bar diameter whichever
more) so as to achieve good bond and corrosion resistance
1064 दीवार Walls
Masonry bearing walls built in mortar as specified in 10632 above unless rationally
designed as reinforced masonry shall not be built of greater height than 15 m subject to a
maximum of four storeys when measured from the mean ground level to the roof slab or
ridge level
The bearing walls in both directions shall be straight and symmetrical in plan as far as
possible
The wall panels formed between cross walls and floors or roof shall be checked for their
strength in bending as a plate or as a vertical strip subjected to the earthquake force acting on
its own mass
Note mdash For panel walls of 200 mm or larger thickness having a storey height not more than
35 metres and laterally supported at the top this check need not be exercised
1065 तचनाई बॉणड Masonry Bond
For achieving full strength of
masonry the usual bonds
specified for masonry should be
followed so that the vertical joints
are broken properly from course
to course To obtain full bond
between perpendicular walls it is
necessary to make a slopping
(stepped) joint by making the
corners first to a height of 600
mm and then building the wall in
between them Otherwise the
toothed joint (as shown in Fig
1014) should be made in both the
walls alternatively in lifts of
about 450 mm
Panel or filler walls in framed buildings shall be properly bonded to surrounding framing
members by means of suitable mortar (as given in 10632 above) or connected through
dowels
Fig 1014 Alternating Toothed Joints in Walls at Corner and T-Junction (IS 4326 1993)
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107 ओपतनोग का परभाव Influence of Openings
Openings are functional necessities in buildings
During earthquake shaking inertia forces act in
the strong direction of some walls and in the weak
direction of others Walls shaken in the weak
direction seek support from the other walls ie
walls B1 and B2 seek support from walls A1 and
A2 for shaking in the direction To be more
specific wall B1 pulls walls A1 and A2 while
wall B2 pushes against them
Thus walls transfer loads to each other at their
junctions (and through the lintel bands and roof)
Hence the masonry courses from the walls
meeting at corners must have good interlocking
(Fig 1015) For this reason openings near the
wall corners are detrimental to good seismic
performance Openings too close to wall corners
hamper the flow of forces from one wall to
another Further large openings weaken walls
from carrying the inertia forces in their own
plane Thus it is best to keep all openings as small as possible and as far away from the corners
as possible
108 धारक दीवारो ो म ओपतनोग परदाि करि की सामानय आवशयकताए General Requirements of
Providing Openings in Bearing Walls
Door and window openings in walls reduce their lateral load resistance and hence should
preferably be small and more centrally located The guidelines on the size and position of
opening are given in Table ndash 104 and in Fig 1016
Fig 1015 Regions of force transfer from weak
walls to strong walls in a masonry building ndash Wall
B1 pulls walls A1 and A2 while wall B2pushes walls
A1 and A2
Fig 1016 Dimensions of Openings and Piers for
Recommendations in Table 3 (IS 4326 1993)
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Table ndash 104 Size and Position of Openings in Bearing Walls
S
No
Position of opening Details of Opening for Building Category
A and B C D and E
1 Distance b5 from the inside corner of outside wall Min Zero mm 230 mm 450 mm
2 For total length of openings the ratio (b1+b2+b3)l1 or
(b6+b7)l2 shall not exceed
a) one-storeyed building
b) two-storeyed building
c) 3 or 4-storeyed building
060
050
042
055
046
037
050
042
033
3 Pier width between consecutive openings b4 Min 340 mm 450 mm 560 mm
4 Vertical distance between two openings one above the
other h3 Min
600 mm 600 mm 600 mm
5 Width of opening of ventilator b8 Max 900 mm 900 mm 900 mm
Openings in any storey shall preferably have their top at the same level so that a continuous
band could be provided over them including the lintels throughout the building
Where openings do not comply with the guidelines as given in Table ndash 104 they should be
strengthened by providing reinforced concrete or reinforcing the brickwork as shown in Fig
1017 with high strength deformed (HSD) bars of 8 mm dia but the quantity of steel shall be
increased at the jambs
If a window or ventilator is to be
projected out the projection shall be in
reinforced masonry or concrete and well
anchored
If an opening is tall from bottom to
almost top of a storey thus dividing the
wall into two portions these portions
shall be reinforced with horizontal
reinforcement of 6 mm diameter bars at
not more than 450 mm intervals one on
inner and one on outer face properly tied
to vertical steel at jambs corners or
junction of walls where used
The use of arches to span over the
openings is a source of weakness and
shall be avoided Otherwise steel ties
should be provided
109 भको पी सदढ़ीकरण वयवसथा Seismic Strengthening Arrangements
All masonry buildings shall be strengthened as specified for various categories of buildings as
listed in Table ndash 105
Fig 1017 Strengthening Masonry around Opening (IS
4326 1993)
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102
Table ndash 105 Strengthening Arrangements Recommended for Masonry Buildings
(Rectangular Masonry Units)(IS 4326 1993)
Building Category Number of Storeyes Strengthening to be Provided in all Storeys
A
i) 1 to 3
ii) 4
a
a b c
B
i) 1 to 3
ii) 4
a b c f g
a b c d f g
C
i) 1 and 2
ii) 3 and 4
a b c f g
a to g
D
i) 1 and 2
ii) 3 and 4
a to g
a to h
E 1 to 3 a to h
Where
a mdash Masonry mortar
b mdash Lintel band
c mdash Roof band and gable band where necessary
d mdash Vertical steel at corners and junctions of walls
e mdash Vertical steel at jambs of openings
f mdash Bracing in plan at tie level of roofs
g mdash Plinth band where necessary and
h mdash Dowel bars
4th storey not allowed in category E
NOTE mdash In case of four storey buildings of category B the requirements of vertical steel may be checked
through a seismic analysis using a design seismic coefficient equal to four times the one given in (a) 3423
of IS 1893 1984 (This is because the brittle behaviour of masonry in the absence of vertical steel results in
much higher effective seismic force than that envisaged in the seismic coefficient provided in the code) If
this analysis shows that vertical steel is not required the designer may take the decision accordingly
The overall strengthening arrangements to be adopted for category D and E buildings which
consist of horizontal bands of reinforcement at critical levels vertical reinforcing bars at corners
junctions of walls and jambs of opening are shown in Fig 1018 amp 1019
Fig 1018 Overall Arrangement of Reinforcing Fig 1019 Overall Arrangement of Reinforcing Masonry
Masonry Buildings (IS 4326 1993) Building having Pitched Roof (IS 4326 1993)
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103
1091 पटट का अनभाग एवो सदढीकरण Section and Reinforcement of Band
The band shall be made of reinforced concrete of grade not leaner than M15 or reinforced
brickwork in cement mortar not leaner than 13 The bands shall be of the full width of the wall
not less than 75 mm in depth and reinforced with steel as indicated in Table ndash 106
Table ndash 106 Recommended Longitudinal Steel in Reinforced Concrete Bands (IS 4326 1993)
Span Building Category
B
Building Category
C
Building Category
D
Building Category
E No of Bars Dia No of Bars Dia No of Bars Dia No of Bars Dia
(1) (2) (3) (4) (5) (6) (7) (8) (9)
m mm mm mm mm
5 or less 2 8 2 8 2 8 2 10
6 2 8 2 8 2 10 2 12
7 2 8 2 10 2 12 4 10
8 2 10 2 12 4 10 4 12
Notes -
1 Span of wall will be the distance between centre lines of its cross walls or buttresses For spans greater than 8 m
it will be desirable to insert pillasters or buttresses to reduce the span or special calculations shall be made to
determine the strength of wall and section of band
2 The number and diameter of bars given above pertain to high strength deformed bars If plain mild-steel bars are
used keeping the same number the following diameters may be used
High Strength Def Bar dia 8 10 12 16 20
Mild Steel Plain bar dia 10 12 16 20 25
3 Width of RC band is assumed same as the thickness of the wall Wall thickness shall be 200 mm minimum A
clear cover of 20 mm from face of wall will be maintained
4 The vertical thickness of RC band be kept 75 mm minimum where two longitudinal bars are specified one on
each face and 150 mm where four bars are specified
5 Concrete mix shall be of grade M15 of IS 456 1978 or 1 2 4 by volume
6 The longitudinal steel bars shall be held in position by steel links or stirrups 6 mm dia spaced at 150 mm apart
NOTE mdash In coastal areas the concrete grade shall be M20 concrete and the filling mortar of 13
(cement-sand with water proofing admixture)
As illustrated in Fig 1020 ndash
In case of reinforced brickwork the
thickness of joints containing steel bars shall
be increased so as to have a minimum
mortar cover of 10 mm around the bar In
bands of reinforced brickwork the area of
steel provided should be equal to that
specified above for reinforced concrete
bands
In category D and E buildings to further
iterate the box action of walls steel dowel
bars may be used at corners and T-junctions
of walls at the sill level of windows to
length of 900 mm from the inside corner in
each wall Such dowel may be in the form of
Fig 1020 Reinforcement and Bending Detail in RC Band ((IS 4326 1993)
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104
U stirrups 8 mm dia Where used such bars must be laid in 13 cement-sand-mortar with a
minimum cover of 10 mm on all sides to minimize corrosion
1010 भको प क दौरान सटोन तचनाई की दीवारो ो का वयविार Behaviour of Stone Masonry
Walls during Earthquakes
Stone has been used in building construction in India since ancient times since it is durable and
locally available The buildings made of thick stone masonry walls (thickness ranges from 600 to
1200 mm) are one of the most deficient building systems from earthquake-resistance point of
view
The main deficiencies include excessive wall thickness absence of any connection between the
two wythes of the wall and use of round stones (instead of shaped ones) (Fig 1021 amp 1022)
Note A wythe is a continuous vertical section of masonry one unit in thickness A wythe may be
independent of or interlocked with the adjoining wythe (s) A single wythe of brick that is not
structural in nature is referred to as a veneer (httpsenwikipediaorgwikiWythe)
The main patterns of earthquake damage include
(a) bulging separation of walls in the horizontal direction into two distinct wythes
(b) separation of walls at corners and T-junctions
(c) separation of poorly constructed roof from walls and eventual collapse of roof and
(d) disintegration of walls and eventual collapse of the whole dwelling
In the 1993 Killari (Maharashtra) earthquake alone over 8000 people died most of them buried
under the rubble of traditional stone masonry dwellings Likewise a majority of the over 13800
deaths during 2001 Bhuj (Gujarat) earthquake is attributed to the collapse of this type of
construction
1011 भको प परतिरोधी सटोन तचनाई भवन क तनमायण िि सामानय तसदाोि General principle for
construction of Earthquake Resistant stone masonry building
10111 भको प परतिरोधी लकषण Earthquake Resistant Features
1 Low strength stone masonry buildings are weak against earthquakes and should be avoided
in high seismic zones Inclusion of special earthquake-resistant features may enhance the
earthquake resistance of these buildings and reduce the loss of life These features include
Fig 1021 Separation of a thick wall into two layers Fig 1022 Separation of unconnected adjacent walls at junction
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105
(a) Ensure proper wall construction
(b) Ensure proper bond in masonry courses
(c) Provide horizontal reinforcing elements
(d) Control on overall dimensions and heights
2 The mortar should be cement-sand (1 6) lime-sand (1 3) or clay mud of good quality
3 The wall thickness should not be larger than 450
mm Preferably it should be about 350 mm and
the stones on the inner and outer wythes should be
interlocked with each other
NOTE - If the two wythes are not interlocked they
tend to delaminate during ground shaking bulge
apart (as shown in Fig 1023) and buckle
separately under vertical load leading to
complete collapse of the wall and the building
4 The masonry should preferably be brought to courses at not more than 600 mm lift
5 lsquoThroughrsquo stones at full length
equal to wall thickness should be
used in every 600 mm lift at not
more than 12 m apart
horizontally If full length stones
are not available stones in pairs
each of about 34 of the wall
thickness may be used in place of
one full length stone so as to
provide an overlap between them
(as shown in Fig 1024)
6 In place of lsquothroughrsquo stones lsquobonding elementsrsquo of steel bars 8 to 10 mm dia bent to S-shape
or as hooked links may be used with a cover of 25 mm from each face of the wall (as shown
in Fig 1024) Alternatively wood-bars of 38 mm X 38 mm cross section or concrete bars of
50 mm X50 mm section with an 8 mm dia rod placed centrally may be used in place of
throughrsquo stones The wood should be well treated with preservative so that it is durable
against weathering and insect action
7 Use of lsquobondingrsquo elements of adequate length should also be made at corners and junctions of
walls to break the vertical joints and provide bonding between perpendicular walls
8 Height of the stone masonry walls (random rubble or half-dressed) should be restricted as
follows with storey height to be kept 30 m maximum and span of walls between cross walls
to be limited to 50 m
Fig 1023 Wall delaminated with buckled
withes (IS 13828 1993)
Fig 1024 Through Stone and Bond Elements (IS 13828 1993)
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106
a) For categories A and B ndash Two storeys with flat roof or one storey plus attic if walls are
built in lime-sand or mud mortar and -one storey higher if walls are built in cement-sand
1 6 mortar
b) For categories C and D - Two storeys with flat roof or two storeys plus attic for pitched
roof if walls are built in 1 6 cement mortar and one storey with flat roof or one storey
plus attic if walls are built in lime-sand or mud mortar respectively
9 If walls longer than 5 m are needed buttresses may be used at intermediate points not farther
apart than 40 m The size of the buttress be kept of uniform thickness Top width should be
equal to the thickness of main wall t and the base width equal to one sixth of wall height
10 The stone masonry dwellings must have horizontal bands (plinth lintel roof and gable
bands) These bands can be constructed out of wood or reinforced concrete and chosen based
on economy It is important to provide at least one band (either lintel band or roof band) in
stone masonry construction
Note Although this type of stone masonry construction practice is deficient with regards to earthquake
resistance its extensive use is likely to continue due to tradition and low cost But to protect human lives
and property in future earthquakes it is necessary to follow proper stone masonry construction in seismic
zones III and higher Also the use of seismic bands is highly recommended
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107
अधयाय Chapter- 11
भकपीय रलयमकन और रटरोफिट ग
SEISMIC EVALUATION AND RETROFITTING
There are considerable number of buildings that do not meet the requirements of current design
standards because of inadequate design or construction errors and need structural upgrading
specially to meet the seismic requirements
Retrofitting is the best solution to strengthen such buildings without replacing them
111 भकपीय रलयमकन SEISMIC EVALUATION
Seismic evaluation is to assess the seismic response of buildings which may be seismically
deficient or earthquake damaged for their future use The evaluation is also helpful in choosing
appropriate retrofitting techniques
The methods available for seismic evaluation of existing buildings can be broadly divided into
two categories
1 Qualitative methods 2 Analytical methods
1111 गणमतरक िरीक QUALITATIVE METHODS
The qualitative methods are based on the available background information of the structures
past performance of similar structures under severe earthquakes visual inspection report some
non-destructive test results etc
Method for Seismic evaluation
Qualitative methods Analytic methods
CapacityDemand
method
Push over
analysis
Inelastic time
history method
Condition
assessment
Visual
inspection
Non-destructive
testing
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The evaluation of any building is a difficult task which requires a wide knowledge about the
structures cause and nature of damage in structures and its components material strength etc
The proposed methodology is divided into three components
1 Condition assessment
It is based on
data collection or information gathering of structures from architectural and structural
drawings
performance characteristics of similar type of buildings in past earthquakes
rapid evaluation of strength drift materials structural components and structural details
2 Visual inspectionField evaluation It is based on observed distress and damage in
structures Visual inspection is more useful for damaged structures however it may also be
conducted for undamaged structures
3 Non-destructive evaluation It is generally carried out for quick estimation of materials
strength determination of the extent of determination and to establish causes remain out of
reach from visual inspection and determination of reinforcement and its location NDT may
also be used for preparation of drawing in case of non-availability
11111 Condition Assessment for Evaluation
The aim of condition assessment of the structure is the collection of information about the
structure and its past performance characteristics to similar type of structure during past
earthquakes and the qualitative evaluation of structure for decision-making purpose More
information can be included if necessary as per requirement
(i) Data collection information gathering
Collection of the data is an important portion for the seismic evaluation of any existing building
The information required for the evaluated building can be divided as follows
Building Data
Architectural structural and construction drawings
Vulnerability parameters number of stories year of construction and total floor area
Specification soil reports and design calculations
Seismicity of the site
Construction Data
Identifications of gravity load resisting system
Identifications of lateral load resisting system
Maintenance addition alteration or modifications in structures
Field surveys of the structurersquos existing condition
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Structural Data
Materials
Structural concept vertical and horizontal irregularities torsional eccentricity pounding
short column and others
Detailing concept ductile detailing special confinement reinforcement
Foundations
Non-structural elements
(ii) Past Performance data
Past performance of similar type of structure during the earthquake provides considerable amount
of information for the building which is under evaluation process Following are the areas of
concerns which are responsible for poor performance of buildings during earthquake
Material concerns
Low grade on concrete
Deterioration in concrete and reinforcement
High cement-sand ratio
Corrosion in reinforcement
Use of recycled steel as reinforcement
Spalling of concrete by the corrosion of embedded reinforcing bars
Corrosion related to insufficient concrete cover
Poor concrete placement and porous concrete
Structural concerns
The relatively low stiffness of the frames excessive inter-storey drifts damage to non-
structural items
Pounding column distress possibly local collapse
Unsymmetrical buildings (U T L V) in plan torsional effects and concentration of damage
at the junctures (ie re-entrant corners)
Unsymmetrical buildings in elevation abrupt change in lateral resistance
Vertical strength discontinuities concentrate damage in the ldquosoftrdquo stories
Short column
Detailing concerns
Large tie spacing in columns lack of confinement of concrete core shear failures
Insufficient column lengths concrete to spall
Locations of inadequate splices brittle shear failure
Insufficient column strength for full moment hinge capacity brittle shear failure
Lack of continuous beam reinforcement hinge formation during load reversals
Inadequate reinforcing of beam column joints or location of beam bar splices at columns
joint failures
Improper bent-up of longitudinal reinforcing in beams as shear reinforcement shear failure
during load reversal
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110
Foundation dowels that are insufficient to develop the capacity of the column steel above
local column distress
(iii) Seismic Evaluation Data
Seismic evaluation of data will provide a general idea about the building performance during an
earthquake The criteria of evaluation of building will depend on materials strength and ductility
of structural components and detailing of reinforcement
Material Evaluation
Buildings height gt 3 stories minimum grade concrete M 20 desirable M 30 to M 40
particularly in columns of lower stories
Maximum grade of steel should be Fe 415 due to adequate ductility
No significant deterioration in reinforcement
No evidence of corrosion or spalling of concrete
Structural components
Evaluation of columns shear strength and drift check for permissible limits
Evaluation of plan irregularities check for torsional forces and concentration of forces
Evaluation of vertical irregularities check for soft storey mass or geometric discontinuities
Evaluation of beam-column joints check for strong column-weak beams
Evaluation of pounding check for drift control or building separation
Evaluation of interaction between frame and infill check for force distribution in frames and
overstressing of frames
(i) Flexural members
Limitation of sectional dimensions
Limitation on minimum and maximum flexural reinforcement at least two continuous
reinforced bars at top and bottom of the members
Restriction of lap splices
Development length requirements for longitudinal bars
Shear reinforcement requirements stirrup and tie hooks tie spacing bar splices
(ii) Columns
Limitation of sectional dimensions
Longitudinal reinforcement requirement
Transverse reinforcement requirements stirrup and tie hooks column tie spacing
column bar splices
Special confining requirements
(iii) Foundation
Column steel doweled into the foundation
Non-structural components
Cornices parapet and appendages are anchored
Exterior cladding and veneer are well anchored
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11112 Field Evaluation Visual Inspection Method
The procedure for visual inspection method is as below
Equipments
Optical magnification allows a detailed view of local areas of distress
Stereomicroscope that allow a three dimensional view of the surface Investigator can
estimate the elevation difference in surface features by calibrating the focus adjustment
screw
Fibrescope and borescopes allow inspection of regions that are inaccessible to the naked eye
Tape to measure the dimension of structure length of cracks
Flashlight to aid in lighting the area to be inspected particularly in post-earthquake
evaluation power failure
Crack comparator to measure the width of cracks at representative locations two types
plastic cards and magnifying lens comparators
Pencil to draw the sketch of cracks
Sketchpad to prepare a representation of wall elevation indicating the location of cracks
spalling or other damage records of significant features such as non-structural elements
Camera for photographs or video tape of the observed cracking
Action
Perform a walk through visual inspection to become familiar with the structure
Gather background documents and information on the design construction maintenance
and operation of structure
Plan the complete investigation
Perform a detailed visual inspection and observe type of damage cracks spalls and
delaminations permanent lateral displacement and buckling or fracture of reinforcement
estimating of drift
Observe damage documented on sketches interpreted to assess the behaviour during
earthquake
Perform any necessary sampling basis for further testing
Data Collection
To identify the location of vertical structural elements columns and walls
To sketch the elevation with sufficient details dimensions openings observed damage such
as cracks spalling and exposed reinforcing bars width of cracks
To take photographs of cracks use marker paint or chalk to highlight the fine cracks or
location of cracks in photographs
Observation of the non-structural elements inter-storey displacement
Limitations
Applicable for surface damage that can be visualised
No identification of inner damage health monitoring of building chang of frequency and
mode shapes
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112
11113 Non-destructive testing (NDT)
Visual inspection has the obvious limitation that only visible surface can be inspected Internal
defects go unnoticed and no quantitative information is obtained about the properties of the
concrete For these reasons a visual inspection is usually supplemented by NDT methods Other
detailed testing is then conducted to determine the extent and to establish causes
NDT tests for condition assessment of structures
Some methods of field and laboratory testing that may assess the minimum concrete strength and
condition and location of the reinforcement in order to characterize the strength safety and
integrity are
(i) Rebound hammer Swiss hammer
The rebound hammer is the most widely used non-destructive device for quick surveys to assess
the quality of concrete In 1948 Ernest Schmidt a Swiss engineer developed a device for testing
concrete based upon the rebound principal strength of in-place concrete comparison of concrete
strength in different locations and provides relative difference in strength only
Limitations
Not give a precise value of compressive strength provide estimate strength for comparison
Sensitive to the quality of concrete carbonation increases the rebound number
More reproducible results from formed surface rather than finished surface smooth hard-
towelled surface giving higher values than a rough-textured surface
Surface moisture and roughness also affect the reading a dry surface results in a higher
rebound number
Not take more than one reading at the same spot
(ii) Penetration resistance method ndash Windsor probe test
Penetration resistance methods are used to determine the quality and compressive strength of in-
situ concrete It is based on the determination of the depth of penetration of probes (steel rods or
pins) into concrete by means of power-actuated driver This provides a measure of the hardness
or penetration resistance of the material that can be related to its strength
Limitations
Both probe penetration and rebound hammer test provide means of estimating the relative
quality of concrete not absolute value of strength of concrete
Probe penetration results are more meaningful than the results of rebound hammer
Because of greater penetration in concrete the prove test results are influenced to a lesser
degree by surface moisture texture and carbonation effect
Probe test may be the cause of minor cracking in concrete
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(iii) Rebar locatorconvert meter
It is used to determine quantity location size and condition of reinforcing steel in concrete It is
also used for verifying the drawing and preparing as-built data if no previous information is
available These devices are based on interaction between the reinforcing bars and low frequency
electromagnetic fields Commercial convert meter can be divided into two classes those based
on the principal of magnetic reluctance and those based on eddy currents
Limitations
Difficult to interpret at heavy congestion of reinforcement or when depth of reinforcement is
too great
Embedded metals sometimes affect the reading
Used to detect the reinforcing bars closest to the face
(iv) Ultrasonic pulse velocity
It is used for determination the elastic constants (modulus of elasticity and Poissonrsquos ratio) and
the density By conducting tests at various points on a structure lower quality concrete can be
identified by its lower pulse velocity Pulse-velocity measurements can detect the presence of
voids of discontinuities within a wall however these measurements can not determine the depth
of voids
Limitations
Moisture content an increase in moisture content increases the pulse velocity
Presence of reinforcement oriented parallel to the pulse propagation direction the pulse may
propagate through the bars and result is an apparent pulse velocity that is higher than that
propagating through concrete
Presence of cracks and voids increases the length of the travel path and result in a longer
travel time
(v) Impact echo
Impact echo is a method for detecting discontinuities within the thickness of a wall An impact-
echo test system is composed of three components an impact source a receiving transducer and
a waveform analyzer or a portable computer with a data acquisition
Limitations
Accuracy of results highly dependent on the skill of the engineer and interpreting the results
The size type sensitivity and natural frequency of the transducer ability of FFT analyzer
also affect the results
Mainly used for concrete structures
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(vi) Spectral analysis of surface waves (SASW)
To assess the thickness and elastic stiffness of material size and location of discontinuities
within the wall such as voids large cracks and delimitations
Limitations
Interpretation of results is very complex
Mainly used on slab and other horizontal surface to determine the stiffness profiles of soil
sites and of flexible and rigid pavement systems measuring the changes in elastic properties
of concrete slab
(vii) Penetrating radar
It is used to detect the location of reinforcing bars cracks voids or other material discontinuities
verify thickness of concrete
Limitations
Mainly used for detecting subsurface condition of slab-on-grade
Not useful for detecting the small difference in materials
Not useful for detecting the size of bars closely spaced bars make difficult to detect features
below the layer of reinforcing steel
1112 ववशलषणमतरक िरीक ANALYTICAL METHODS
Analytical methods are based on considering capacity and ductility of the buildings which are
based on detailed dynamic analysis of buildings The methods in this category are
capacitydemand method pushover analysis inelastic time history analysis etc Brief discussions
on the method of evaluation are as follows
11121 CapacityDemand (CD) method
The forces and displacements resulting from an elastic analysis for design earthquake are
called demand
These are compared with the capacity of different members to resist these forces and
displacements
A (CD) ratio less than one indicate member failure and thus needs retrofitting
When the ductility is considered in the section the demand capacity ratio can be equated to
section ductility demand of 2 or 3
The main difficulty encountered in using this method is that there is no relationship between
member and structure ductility factor because of non-linear behaviour
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11122 Push Over Analysis
The push over analysis of a structure is a static non-linear analysis under permanent vertical
loads and gradually increasing lateral loads
The equivalent static lateral loads approximately represent earthquake-induced forces
A plot of total base shear verses top displacement in a structure is obtained by this analysis
that would indicate any premature failure or weakness
The analysis is carried out up to failure thus it enables determination of collapse load and
ductility capacity
On a building frame loaddisplacement is applied incrementally the formation of plastic
hinges stiffness degradation and plastic rotation is monitored and lateral inelastic force
versus displacement response for the complete structure is analytically computed
This type of analysis enables weakness in the structure to be identified The decision to
retrofit can be taken on the basis of such studies
11123 Inelastic time-history analysis
A seismically deficient building will be subjected to inelastic action during design earthquake
motion
The inelastic time history analysis of the building under strong ground motion brings out the
regions of weakness and ductility demand in the structure
This is the most rational method available for assessing building performance
There are computer programs available to perform this type of analysis
However there are complexities with regard to biaxial inelastic response of columns
modelling of joints behaviour interaction of flexural and shear strength and modelling of
degrading characteristics of member
The methodology is used to ascertain deficiency and post-elastic response under strong
ground shaking
Fig ndash 111 Strengthening strategies
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112 भवनो की रटरोफिट ग Retrofitting of Building
Retrofitting is to upgrade the strength and structural capacity of an existing structure to enable it
to safely withstand the effect of strong earthquakes in future
1121 सकटरचरल लवल यम गलोबल रटरोफि िरीक Structural Level or Global Retrofit
Methods
Two approaches are used for structural-level retrofitting
(i) Conventional Methods
(ii) Non-conventional methods
Retrofit procedure
Detailed seismic
evaluation
Retrofit
techniques
Seismic capacity
assessment
Selection of retrofit
scheme
Design of retrofit
scheme and detailing
Re-evaluation of
retrofit structure
Addition of infill walls
Addition of new
external walls
Addition of bracing
systems
Construction of wing
walls
Strengthening of
weak elements
Structural Level or Global Member Level or Local
Seismic Base Isolation
Jacketing of beams
Jacketing of columns
Jacketing of beam-
column joints
Strengthening of
individual footings
Seismic Dampers
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11211 Conventional Methods
Conventional Methods are based on increasing the seismic resistance of existing structure The
main categories of these methods are as follow
a) Addition of infilled walls
b) Addition of new external walls
c) Addition of bracing system
d) Construction of wing walls
e) Strengthening of weak elements
112111 Addition of infilled walls
The construction of infill walls within the frames of the load bearing structures as shown in the
example of Fig ndash 112 aims to drastically increase the strength and the stiffness of the structure
This method can also be applied in order to correct design errors in the structure and more
specifically when a large asymmetric distribution of strength or stiffness in elevation or an
eccentricity of stiffness in plan have been recognised
Fig - 112 Addition of infilled wall and wing walls
Fig - 113 Frames and shear wall
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As shown in Fig ndash 114 there are two alternatives methods of adding infill walls Either the infill
wall is simply placed between two existing columns or it is extended around the columns to form
a jacket The second method is specifically recommended in order to increase the strength in this
region In the situation where the existing columns are very weak a steel cage should be placed
around the columns before constructing new walls and column jackets In all cases the base of
any new wall should always be connected to the existing foundation
112112 Addition of new external walls
In some cases strengthening by adding concrete walls can be performed externally This can
often be carried out for functional reasons as for example in cases when the building must be
kept in operation during the intervention works New cast-in-place concrete walls constructed
outside the building can be designed to resist part or all the total seismic forces induced in the
building The new walls are preferably positioned adjacent to vertical elements (columns or
walls) of the building and are connected to the structure by placing special compression tensile
or shear connectors at every floor level of the building As shown in Figure 115 new walls
usually have a L-shaped cross-section and are constructed to be in contact with the external
corners of the building
Fig ndash 114 Two alternative methods of adding infill walls
Fig ndash 115 Schematic arrangement of connections between the existing building and
a new wall (a) plan (b) section of compression connector and (c) section of tension
connector
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It is important to ensure that connectors behave elastically under seismic design action effects
For this reason when designing the connectors a resistance safety factor equal to 14 is
recommended The use of compression and tensile connectors instead of shear connectors is
strongly recommended as much higher forces can be transferred It is essential that the anchorage
areas for the connectors on the existing
building and on the new walls have
enough strength to guarantee the transfer
of forces between new walls and the
existing structures
A very important issue of the above
method concerns the foundation of new
walls Foundation conditions should be
improved if large axial forces can be
induced in new walls during seismic
excitation In addition the construction
of short cantilever beams protruding from
the wall underneath the adjacent beams
at every floor level of the building as
shown in Fig ndash 116 appears to be a good solution
112113 Addition of bracing systems
The construction of bracing within
the frames of the load bearing
structure aims for a high increase
in the stiffness and a considerable
increase in the strength and
ductility of the structure Bracing
is normally constructed from steel
elements rather than reinforced
concrete as the elastic
deformation of steel aids the
absorption of seismic energy
Bracing systems can be used in a similar way as that for
steel constructions and can be applied easily in single-
storey industrial buildings with a soft storey ground floor
level where no or few brick masonry walls exist between
columns
Various truss configurations have been applied in
practice examples of which are K-shaped diamond
shaped or cross diagonal The latter is the most common
and is often the most effective solution
Fig ndash 116 Construction of cantilever beams to
transfer axial forces to new walls (a) plan (b)
section c-c
Fig ndash 117 Reinforced Concrete Building retrofitted
with steel bracing
Fig ndash 118 Steel bracing soft storey
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Use of steel bracing has a potential advantage over other schemes for the following reasons
Higher strength and stiffness can be proved
Opening for natural light can be
made easily
Amount of work is less since
foundation cost may be minimised
Bracing system adds much less
weight to the existing structure
Most of the retrofitting work can
be performed with prefabricated
elements and disturbance to the
occupants may be minimised
112114 Construction of wing wall
The construction of reinforced
concrete wing walls in continuous
connection with the existing columns
of a structure as shown above in
example of Fig ndash 112 is a very
popular technique
As presented in Fig ndash 1110 there are
two alternative methods of connecting
the wing wall to the existing load
bearing structure
In the first method the wall is connected to the column and the beams at the top and the base
of any floor level Steel dowels or special anchors are used for the connection and the
reinforcement of the new wall is welded to the existing reinforcement
In the second method the new wing wall is extended around the column to form a jacket
Obviously in this case stresses at the interface between the new concrete and the existing
column are considerably lower when compared to the first method
Moreover uncertainties regarding the capacity of the connection between the wall and the
column do not affect the seismic performance of the strengthened element Therefore the second
alternative method is strongly recommended
Fig ndash 1110 Construction of reinforced concrete wing
wall
Fig ndash 119 Steel bracing
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112115 Strengthening weak elements
The selective strengthening of weak elements of the
structure aims to avoid a premature failure of the critical
elements of a building and to increase the ductility of the
structure
Usually this method is applied to vertical elements and
is accompanied by the construction of fibre reinforced
polymer (FRP) jackets or as shown in Fig- 1111 steel
cages around the vertical elements
If a strength increase is also required this method can
include the construction of column jackets of shotcrete
or reinforced concrete
11212 Non-conventional methods
These are based on reduction of seismic demands Seismic demands are the force and
displacement resulting from an elastic analysis for earthquake design Incorporation of energy
absorbing systems to reduce seismic demands are as follows
(i) Seismic Base Isolation
(ii) Seismic Dampers
112121 Seismic Base Isolation
Isolation of
superstructure from the
foundation is known as
base isolation
It is the most powerful
tool for passive
structural vibration
control technique
Types of base isolations
Elastomeric Bearings
This is the most widely used Base Isolator
The elastomer is made of either Natural Rubber or Neoprene
The structure is decoupled from the horizontal components of the earthquake ground motion
Fig ndash 1111 Construction of a steel
cage around a vertical element
Fig ndash 1112 Base isolated structures
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Sliding System
a) Sliding Base Isolation Systems
It is the second basic type of isolators
This works by limiting the base shear across the
isolator interface
b) Spherical Sliding Base Isolators
The structure is supported by bearing pads that
have curved surface and low friction
During an earthquake the building is free to
slide on the bearings
c) Friction Pendulum Bearing
These are specially designed base isolators
which works on the
principle of simple
pendulum
It increases the natural time
period of oscillation by
causing the structure to
Fig ndash 1113 Elastomeric Isolators Fig ndash 1114 Steel Reinforced Elastomeric
Isolators
Fig ndash 1115 Metallic Roller Bearing
Fig ndash 1116 Spherical Sliding Base
Isolators
Fig ndash 1117 Cross-section of Friction Pendulum Bearing
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slide along the concave inner surface through the frictional interface
It also possesses a re-centering capability
Typically bearings measure 10 m (3 feet) in dia 200 mm (8 inches) in height and weight
being 2000 pounds
d) Advantages of base isolation
Isolate building from ground motion
Building can remain serviceable throughout construction
Lesser seismic loads hence lesser damage to the structure
Minimal repair of superstructure
Does not involve major intrusion upon existing superstructure
e) Disadvantages of base isolation
Expensive
Cannot be applied partially to structures unlike other retrofitting
Challenging to implement in an efficient manner
Allowance for building displacements
Inefficient for high rise buildings
Not suitable for buildings rested on soft soil
112122 Seismic Dampers
Seismic dampers are used in place of structural elements like diagonal braces for controlling
seismic damage in structures
It partly absorbs the seismic energy and reduces the motion of buildings
Types
Viscous Dampers Energy is absorbed by silicon-based fluid passing between piston-
cylinder arrangement
Fig -1118 Cross-section of a Viscous Fluid Damper
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Friction Dampers Energy is absorbed
by surfaces with friction between
rubbing against each other
Yielding Dampers Energy is absorbed
by metallic components that yield
1122 सदसकय सकिर यम सकथमनीय ररटरोफमइ िरीक Member Level or Local Retrofit Methods
The member level retrofit or local retrofit approach is to upgrade the strength of the members
which are seismically deficient This approach is more cost effective as compared to the
structural level retrofit
Jacketing
The most common method of enhancing the individual member strength is jacketing It includes
the addition of concrete steel or fibre reinforced polymer (FRP) jackets for use in confining
reinforced concrete columns beams joints and foundation
Types of jacketing
(1) Concrete jacketing (2) Steel jacketing (3) Strap jacketing
Fig ndash 1119 Friction Dampers
Fig ndash 1120 Yielding Dampers
Fig ndash 1121 Type of Jacketing
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11221 Member level Jacketing
(i) Jacketing of Columns
Different methods of column jacketing are as shown in Figures below
Fig ndash 1122 (b) Column with
CFRP (Carbon Fibre
Reinforced Polymer) Wrap
Fig ndash 1122 (c) Column with Steel Fig ndash 1122 (d) Column with
Jacketing Steel Caging
Fig ndash 1122 (a) Reinforced Concrete Jacketing
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Fig ndash 1122 (e) Construction techniques for Fig ndash 1122 (f) Local strengthening of RC
column jacketing Columns
Fig ndash 1122 (g) Details for provision of longitudinal reinforcement
Fig ndash 1122 (h) Different methods of column jacketing
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(ii) Jacketing of Beam
(iii) Jacketing of Beam-Column Joint
Fig ndash 1123 Different ways of beam jacketing
Fig ndash 1124 Continuity of longitudinal steel in jacketed beams
Fig ndash 1125 Steel cage assembled in the joint
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11222 Table showing the details of reinforced concrete jacketing
Properties of jackets match with the concrete of the existing structure
compressive strength greater than that of the existing
structures by 5 Nmm2 (50 kgcm
2) or at least equal to that
of the existing structure
Minimum width of
jacket 10 cm for concrete cast-in-place and 4 cm for shotcrete
If possible four sided jacket should be used
A monolithic behaviour of the composite column should be
assured
Narrow gap should be provided to prevent any possible
increase in flexural capacity
Minimum area of
longitudinal
reinforcement
3Afy where A is the area of contact in cm2 and fy is in
kgcm2
Spacing should not exceed six times of the width of the new
elements (the jacket in the case) up to the limit of 60 cm
Percentage of steel in the jacket with respect to the jacket
area should be limited between 0015 and 004
At least a 12 mm bar should be used at every corner for a
four sided jacket
Minimum area of
transverse
reinforcement
Designed and spaced as per earthquake design practice
Minimum bar diameter used for ties is not less than 10 mm
diameter anchorage
Due to the difficulty of manufacturing 135 degree hooks on
the field ties made up of multiple pieces can be used
Shear stress in the
interface Provide adequate shear transfer mechanism to assured
monolithic behaviour
A relative movement between both concrete interfaces
(between the jacket and the existing element) should be
prevented
Chipping the concrete cover of the original member and
roughening its surface may improve the bond between the
old and the new concrete
For four sided jacket the ties should be used to confine and
for shear reinforcement to the composite element
For 1 2 3 side jackets as shown in Figures special
reinforcement should be provided to enhance a monolithic
behaviour
Connectors Connectors should be anchored in both the concrete such that
it may develop at least 80 of their yielding stress
Distributed uniformly around the interface avoiding
concentration in specific locations
It is better to use reinforced bars (rebar) anchored with epoxy
resins of grouts as shown in Figure (a)
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11223 Practical aspects in choosing appropriate techniques
Certain issues of practical importance that may help to avoid mistakes in choosing the
appropriate technique are as follows
1) The strengthening of columns by using FRPs or steel jackets is unsuitable for flexible
structures where failure would be controlled by deflection In this case the strengthening
should aim to increase the stiffness
2) It is not favourable to use steel cages or confine with FRPs when an increase in the flexural
capacity of vertical elements is required
3) The application of confinement (with FRPs or steel) to circular or rectangular columns would
increase the ductility and the shear strength and would limit the slippage of overlapping bars
when the lap length has been found to be insufficient However a significant contribution
cannot be expected for columns of rectangular cross section with a large aspect ratio or those
with L-shaped cross sections
4) In the case of columns that have heavily rusted reinforcement strengthening with FRP
jackets (or the application of epoxy glue) will protect the reinforcement from further
oxidation However if the corrosion of the reinforcement is at an advanced stage it is
probable that strengthening may not stop the premature failure of the element
5) The construction of FRP jackets around vertical elements will increase the ductility but it
cannot increase the buckling resistance of the longitudinal reinforcement bars Thus if the
stirrups are too thin in an existing element failure will probably result from the premature
bending of the vertical reinforcement In this case local stress concentrations from the
distressed bars will build up between the stirrups and will lead to a local failure of the jacket
Consequently if bending of the vertical reinforcement has been evaluated as the most likely
cause of column failure the preferable choice for strengthening of the element would be to
place a steel cage
6) In areas where the overlapping of reinforcement bars has been found to be inadequate (short
lap lengths) confining the element with FRPs steel cages or steel jackets will improve the
strength and the ductility of the region considerably However even if it improved the
behaviour it is eventually unfeasible to deter the slipping of bars Consequently when the lap
length of bars has been found to be smaller than 30 of code requirements the solution of
welding of bars must be selected Moreover it must be pointed out that confinement cannot
offer anything to longitudinal bars that are not in the corners of the cross section
7) Experimentally the procedure of placing FRP sheets to strengthen weak beam-column joints
has proved to be particularly effective In practice however this technique has been found to
be difficult to apply due to the presence of slabs and transverse beams The same problems
arise when placing steel plates Other techniques such as the construction of reinforced
concrete jackets or the reconstruction of joints with additional interior reinforcement appear
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to be more beneficial In cases where only a light damage to the joints has been found
repairing with an epoxy resin appears to be particularly effective solution
8) The placing of new concrete in contact with an existing element (by shotcreting and
especially by pouring) will require prior aggravation of the old surface to a depth of at least 6
mm This should be performed by sandblasting or by using suitable mechanical equipment
(for example a scabbler and not just simply a hammer and a chisel) This is to remove the
exterior weak skin of the concrete and to expose the aggregate
9) When placing a new concrete jacket around an existing column it is not always possible to
follow code requirements and place
internal rectangular stirrups to enclose
the middle longitudinal bars as shown
in Fig-1126(a) In this case it is
proposed to place two middle bars in
each side of the jacket so that
octagonal stirrups can be easily
placed as demonstrated in
Fig-1126(b)
In the case where columns have a cross section
with a large aspect ratio the middle longitudinal
bars can be connected by drilling holes through
the section in order to place a S-shaped stirrup as
shown in Fig ndash 1127 After placing stirrups the
remaining void can be filled with epoxy resin In
order to ease placement the S-shaped stirrup can
be prefabricated with one hook and after placing
the second hook can be formed by hand
10) If a thin concrete jacket is to be
placed around a vertical element
and the 135 deg hooks at the ends
of the stirrups are impeded by the
old column it would be
acceptable to decrease the hook
anchorage from 10 times the bar
diameter to 5 or 6 times the bar
diameter as shown in
Fig ndash 1128(a) Otherwise the
ends the stirrups should be
welded together or connected
with special contacts (clamps) as
presented in Fig ndash 1128(b) that have now appeared on the market
(a) (b)
Fig ndash 1126 Placement of internal stirrups in
rectangular cross section
Fig ndash 1127 Placement of an internal
stirrup in a rectangular cross section
with a large aspect ratio
(a) (b)
Fig ndash 1128 Reducing hook lengths and welding the
ends of stirrups
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11) When constructing a jacket around a column it is
important to also strengthen the column joint As shown
in Fig ndash 1129 this can be accomplished by where
possible extending the longitudinal reinforcement bars
around the joint In addition as also shown in
Fig ndash 1129 stirrups must be placed in order to confine
the concrete of the jacket around the joint
In the case where the joint has been found to be
particularly weak a steel diagonal collar can be placed
around the joint before placing the reinforcement as
shown in Fig ndash 1130
12) It is preferable that a new concrete jacket is placed
continuously from the foundation to the top of the building
If this is not possible (due to maintaining the functioning of
the building) it is usual to stop the jacket at the top of the
ground floor level In this case there is a need to anchor the
jacketrsquos longitudinal bars to the existing column This can
be achieved by anchoring a steel plate to the base of the
column of the floor level above and then welding the
longitudinal bars to the anchor plate as shown in Fig ndash
1131
13) In the case where there is a need to reconstruct a heavily damaged column after first shoring
up the column all the defective concrete must be removed so that only good concrete
Fig ndash 1129 Strengthening the
column joint
Fig ndash 1130 Placing a steel diagonal collar
around a weak column joint
Fig ndash 1131 Removal of
defective concrete from a
heavily damaged column
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remains as shown in Fig ndash 1132 Any
buckled reinforcement bars must be welded
to the existing bars Finally the column can
be recast by placing a special non-shrink
concrete
14) In order to anchor new reinforcement bars dowels or anchors with the use of epoxy glue the
diameter of holes drilled into the existing concrete should be roughly 4 mm larger than the
diameter of the bar The best way to remove dust from drilled holes would be to spray water
at the back of the hole The best results (higher adhesive forces) are achieved when the walls
of the hole have been roughened slightly with a small wire brush
15) Care is required when shotcreting in the presence of reinforcement There is a danger of an
accumulation of material building up behind the bars This is usually accredited to material
sticking to the face of bars and may be due to either a low velocity a large firing distance or
insufficient pressure from the compressor
16) The placing of steel plates and especially FRP sheets or fabrics requires special preparation of
the concrete surface to which they will be stuck The rounding of corners and the removal of
surface abnormalities constitute minimal conditions for the application of this technique
17) Two constructional issues that concern the connection of new walls to the old frame require
particular attention The first problem is due to the shrinkage of the new concrete and the
appearance of cracks at the top of the new wall immediately below the old beam in the
region where a good contact between surfaces is essential Here the problem of shrinkage
can be usually dealt with by placing concrete of a particular composition where special
admixtures (for example expansive cements) have been used Alternatively the new wall
could be placed to about 20 cm below the existing beam and after more than 7 days (taking
into account temperature and how new concrete shrinks with time) the void can be filled
with an epoxy or polyster mortar In some cases depending on site conditions (ease of access
dry conditions etc) the new wall can be placed to a height of 2 to 5 mm below the beam and
the void filled with resin glue using the technique of resin injection The second problem
concerns the case of walls from ready-mix concrete and the difficulty of placing the higher
part of the wall due to insufficient access For this reason alone the use of shotcrete should
be the preferred option
Fig ndash 1132 Welding longitudinal bars to an
anchor plate
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113 आरसी भवनो क घ को र समरमनय भकपी कषतियम और उनक उपचमर Common
seismic damage in components of RC Buildings and their remedies
Possible damages in component of RC Buildings which are frequently observed after the
earthquakes are as follows
(i) R C Column
The most common modes of failure of column are as follows
Mode -1 Formation of plastic hinge at the base of ground level columns
Mechanism The column when subjected to seismic
motion its concrete begins to disintegrate and the
load carried by the concrete shifts to longitudinal
reinforcement of the column This additional load
causes buckling of longitudinal reinforcement As a
result the column shortens and looses its ability to
carry even the gravity load
Reasons Insufficient confinement length and
improper confinement in plastic hinge region due to
smaller numbers of ties
Remedies This type of damage is sensitive to the cyclic moments generated during the
earthquake and axial load intensity Consideration is to be paid on plastic hinge length or length
of confinement
Mode ndash 2 Diagonal shear cracking in mid span of columns
Mechanism In older reinforced
concrete building frames column
failures were more frequent since
the strength of beams in such
constructions was kept higher than
that of the columns This shear
failure brings forth loss of axial
load carrying capacity of the
column As the axial capacity
diminishes the gravity loads carried by the column are transferred to neighbouring elements
resulting in massive internal redistribution of forces which is also amplified by dynamic effects
causing spectacular collapse of building
Reason Wide spacing of transverse reinforcement
Remedies To improve understanding of shear strength as well as to understand how the gravity
loads will be supported after a column fails in shear
Fig ndash 1133 Formation of plastic hinge at
the base
Fig ndash 1134 Diagonal shear cracking in mid span of
columns
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Mode ndash 3 Shear and splice failure of longitudinal reinforcement
Mechanism Splices of column
longitudinal reinforcement in
older buildings were
commonly designed for
compression only with
relatively light transverse
reinforcement enclosing the
lap
Under earthquake motion the
longitudinal reinforcement may
be subjected to significant tensile stresses which require lap lengths for tension substantially
exceeding those for compression As a result slip occurs along the splice length with spalling of
concrete
Reasons Deficient lap splices length of column longitudinal reinforcement with lightly spaced
transverse reinforcement particularly if the splices just above the floor slab especially the splices
just above the floor slab which is very common in older construction
Remedies Lap splices should be provided only in the center half of the member length and it
should be proportionate to tension splice Spacing of transverse reinforcement as per IS
139291993
Mode ndash 4 Shear failures in captive columns and short columns
Captive column Column whose deforming ability is restricted and only a fraction of its height
can deform laterally It is due to presence of adjoining non-structural elements columns at
slopping ground partially buried basements etc
Fig - 1135 Shear and splice failure of longitudinal
reinforcement
Fig ndash 1136 Restriction to the Lateral
Displacement of a Column Creating a Captive-
Column Effect
Fig ndash 1137 Captive-column effect in a
building on sloping terrain
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A captive column is full storey slender column whose clear height is reduced by its part-height
contact with a relatively stiff non-structural element such as a masonry infill wall which
constraints its lateral deformation over
the height of contract
The captive column effect is caused by
a non-intended modification to the
original structural configuration of the
column that restricts the ability of the
column to deform laterally by partially
confining it with building components
The column is kept ldquocaptiverdquo by these
components and only a fraction of its
height can deform laterally
corresponding to the ldquofreerdquo portion
thus the term captive column Figure
as given below shows this situation
Short column Column is made shorter than neighbouring column by horizontal structural
elements such as beams girder stair way landing slabs use of grade beams and ramps
Fig ndash 1138 Typical captive-column failure Fig ndash 1139 Column damage due to
captive- column effect
Fig ndash 1140 Captive column caused by ventilation
openings in a partially buried basement
Fig ndash 1141 Short column created by
a stairway landing
Fig ndash 1142 Shear failures in captive columns
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For split-level buildings in order to circumvent the short-column effect the architect should
avoid locating a frame at the vertical plane where the transition between levels occurs For
buildings on slopes special care should be exercised to locate the sloping retaining walls in such
a way that no captive-column effects are induced Where stiff non-structural walls are still
employed these walls should be separated from the structure and in no case can they be
interrupted before reaching the full height of the adjoining columns
Mechanism A reduction in the clear height of captive or short columns increases the lateral
stiffness Therefore these columns are subjected to larger shear force during the earthquake since
the storey shear is distributed in proportion to lateral stiffness of the same floor If these columns
reinforced with conventional longitudinal and transverse reinforcement and subjected to
relatively high axial loading fail by splitting of concrete along their diagonals if the axial
loading level is low the most probable mode of failure is by shear sliding along full depth cracks
at the member ends Moreover in the case of captive column is so effective that usually damage
is shifted to the short non-confined upper section of the column
Reasons Large shear stresses when the structure is subjected to lateral forces are not accounted
for in the standard frame design procedure
Remedies The best solution for captive column or short column is to avoid the situation
otherwise use separation gap in between the non-structural elements and vertical structural
element with appropriate measures against out-of-plane stability of the masonry wall
(ii) R C Beams
The shear-flexure mode of failure is most commonly observed during the earthquakes which is
described as below
Mode ndash 5 Shear-flexure failure
Mechanism Two types of plastic hinges may form in the beams of multi-storied framed
construction depending upon the span of
beams In case of short beams or where
gravity load supported by the beam is
low plastic hinges are formed at the
column ends and damage occurs in the
form of opening of a crack at the end of
beam otherwise there is formation of
plastic hinges at and near end region of
beam in the form of diagonal shear
cracking
Reasons Lack of longitudinal compressive reinforcement infrequent transverse reinforcement in
plastic hinge zone bad anchorage of the bottom reinforcement in to the support or dip of the
longitudinal beam reinforcement bottom steel termination at face of column
Fig ndash 1143 Shear-flexure failure
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Remedies Adequate flexural and shear strength must be provided and verification by design
calculation is essential The beams should not be too stiff with respect to adjacent columns so
that the plastic hinging will occur in beam rather than in column To ensure that the plastic hinges
zones in beams have adequate ductility the following considerations must be considered
Lower and upper limits on the amount of longitudinal flexural tension steel
A limit on the ration of the steel on one side of the beam to that of on the other side
Minimum requirements for the spacing and size of stirrups to restrain buckling of the
longitudinal reinforcement
(iii) R C Beam-Column Joints
The most common modes of failure in beam-column joint are as follows
Mode ndash 6 shear failure in beam-column joint
Mechanism The most common
failure observed in exterior joints are
due to either high shear or bond
(anchorage) under severe
earthquakes Plastic hinges are
formed in the beams at the column
faces As a result cracks develop
throughout the overall beam depth
Bond deterioration near the face of
the column causes propagation of
beam reinforcement yielding in the joint and a shortening of the bar length available for force
transfer by bond causing horizontal bar slippage in the joint In the interior joint the beam
reinforcement at both the column faces undergoes different stress conditions (compression and
tension) because of opposite sights of seismic bending moments results in failure of joint core
Reasons Inadequate anchorage of flexural steel in beams lack of transverse reinforcement
Remedies Exterior Joint ndash The provision on anchorage stub for the beam reinforcement
improves the performance of external joints by preventing spalling of concrete cover on the
outside face resulting in loss of flexural strength of the column This increases diagonal strut
action as well as reduces steel congestion as the beam bars can be anchored clear of the column
bars
(iv) R C Slab
Generally slab on beams performed well during earthquakes and are not dangerous but cracks in
slab creates serious aesthetic and functional problems It reduces the available strength stiffness
and energy dissipation capacity of building for future earthquake In flat slab construction
punching shear is the primary cause of failure The common modes of failure are
Fig - 1144 Shear failure in beam-column joint
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Mode ndash 7 Shear cracking in slabs
Mechanism Damage to slab oftenly
occurs due to irregularities such as large
openings at concentration of earthquake
forces close to widely spaced shear
walls at the staircase flight landings
Reasons Existing micro cracks which
widen due to shaking differential
settlement
Remedies
Use secondary reinforcement in the bottom of the slab
Avoid the use of flat slab in high seismic zones provided this is done in conjunction with a
stiff lateral load resisting system
(v) R C Shear Walls
Shear walls generally performed well during the earthquakes Four types of failure modes are
generally observed
Mode ndash 8 Four types of failure modes are generally observed
(i) Diagonal tension-compression failure in the form of cross-shaped shear cracking
(ii) Sliding shear failure cracking at interface of new and old concrete
(iii) Flexure and compression in bottom end region of wall and finally
(iv) Diagonal tension in the form of X shaped cracking in coupling beams
Fig ndash 1145 Shear cracking in slabs
Fig ndash 1146 Diagonal tension-compression Sliding shear Flexure and compression
failure
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Mechanism Shear walls are subjected to shear and flexural deformation depending upon the
slenderness ratio Therefore the damage in shear walls may generally occurs due to inadequate
shear and flexure capacity of wall Slender walls are governed by their flexural strength and
cracking occurs in the form of yielding of main flexure reinforcement in the plastic hinge region
normally at the base of the wall Squat walls are governed by their shear strength and failure
takes place due to diagonal tension or diagonal compression in the form of inclined cracking
Coupling beams between shear walls or piers may also damage due to inadequate shear and
flexure capacity Sometimes damage occurs at the construction joints in the form of slippage and
related drift
Reasons
Flexuralboundary compression failure Inadequate transverse confining reinforcement to the
main flexural reinforcement near the outer edge of wall in boundary elements
Flexurediagonal tension Inadequate horizontal shear reinforcement
Sliding shear Absence of diagonal reinforcement across the potential sliding planes of the
plastic hinge zone
Coupling beams Inadequate stirrup reinforcement and no diagonal reinforcement
Construction joint Improper bonding between two surfaces
Remedies
The concrete shear walls must have boundary elements or columns thicker than walls which
will carry the vertical load after shear failure of wall
A proper connection between wall versus diaphragm as well as wall versus foundation to
complete the load path
Proper bonding at construction joint in the form of shear friction reinforcement
Provision of diagonal steel in the coupling beam
Fig ndash 1147 Diagonal tension in the form of X shaped
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(v) Infill Walls
Infill panels in reinforced concrete frames are the cause of unequal distribution of lateral forces
in the different frames of a building producing vertical and horizontal irregularities etc the
common mode of failure of infill masonry are in plane or shear failure
Mode ndash 9 Shear failure of masonry infill
Mechanism Frame with infill possesses much more lateral stiffness than the bare frame and
hence initially attracts most of the lateral force during an earthquake Being brittle the infill
starts to disintegrate as soon as its strength is reached Infills that were not adequately tied to the
surrounding frames sometimes dislodges by out-of-plane seismic excitations
Reasons Infill causes asymmetry of load application resulting in increased torsional forces and
changes in the distribution of shear forces between lateral load resisting system
Remedies Two strategies are possible either complete separation between infill walls and frame
by providing separation joint so that the two systems do not interact or complete anchoring
between frame and infill to act as an integral unit Horizontal and vertical reinforcement may also
be used to improve the strength stiffness and deformability of masonry infill walls
(vi) Parapets
Un-reinforced concrete parapets with large height-to-thickness ratio and not in proper anchoring
to the roof diaphragm may also constitute a hazard The hazard posed by a parapet increases in
direct proportion to its height above building base which has been generally observed
The common mode of failure of parapet wall is against out-of-plane forces which is described as
follows
Mode ndash 10 Brittle flexure out-of-plane failure
Mechanism Parapet walls are acceleration sensitive in the out-of-plane direction the result is
that they may become disengaged and topple
Fig ndash 1148 Shear failure of masonry infill
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Reasons Not properly braced
Remedies Analysed for acceleration forces and braced and connected with roof diaphragm
114 चचनमई सरचनमओ की रटरोफिट ग Retrofitting of Masonry Structures
(a) Principle of Seismic Safety of Masonry Buildings
Integral box action
Integrity of various components
- Roof to wall
- Wall to wall at corners
- Wall to foundation
Limit on openings
(b) Methods for Retrofitting of Masonry Buildings
Repairing (Improving existing masonry strength)
Stitching of cracks
Grouting with cement or epoxy
Use of CFRP (Carbon Fibre Reinforced Polymer) strips
Fig ndash 1149 Brittle flexure out-of-plane failure
(a) (b)
Fig ndash 1150 (a) Stitching of cracks Fig ndash 1150 (b) Repair of damaged member in
masonry walls
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(c) Retrofitting of Earthquake vulnerable buildings
External binding or jacketing
Shotcreting
Strengthening of wall intersections
Strengthening by cross wall
Strengthening by buttresses
Strengthening of arches
Fig ndash 1151 Integral Box action
(a) (b)
Fig - 1152 (a) Strengthening of Wall Fig - 1152 (b) Strengthening by
intersections cross wall
(a) (b)
Fig ndash 1153 (a) Strengthening by Fig ndash 1153 (b) Strengthening of Arches
Buttresses
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पररलिष Annexure ndash I
भारिीय भको पी सोतििाएा Indian Seismic Codes
Development of building codes in India started rather early Today India has a fairly good range
of seismic codes covering a variety of structures ranging from mud or low strength masonry
houses to modern buildings However the key to ensuring earthquake safety lies in having a
robust mechanism that enforces and implements these design code provisions in actual
constructions
भको पी तिजाइन कोि का मितव Importance of Seismic Design Codes
Ground vibrations during earthquakes cause forces and deformations in structures Structures
need to be designed to withstand such forces and deformations Seismic codes help to improve
the behaviour of structures so that they may withstand the earthquake effects without significant
loss of life and property An earthquake-resistant building has four virtues in it namely
(a) Good Structural Configuration Its size shape and structural system carrying loads are such
that they ensure a direct and smooth flow of inertia forces to the ground
(b) Lateral Strength The maximum lateral (horizontal) force that it can resist is such that the
damage induced in it does not result in collapse
(c) Adequate Stiffness Its lateral load resisting system is such that the earthquake-induced
deformations in it do not damage its contents under low-to moderate shaking
(d) Good Ductility Its capacity to undergo large deformations under severe earthquake shaking
even after yielding is improved by favourable design and detailing strategies
Seismic codes cover all these aspects
भारिीय भको पी सोतििाएा Indian Seismic Codes
Seismic codes are unique to a particular region or country They take into account the local
seismology accepted level of seismic risk building typologies and materials and methods used
in construction The first formal seismic code in India namely IS 1893 was published in 1962
Today the Bureau of Indian Standards (BIS) has the following seismic codes
1 IS 1893 (Part I) 2002 Indian Standard Criteria for Earthquake Resistant Design of
Structures (5 Revision)
2 IS 4326 1993 Indian Standard Code of Practice for Earthquake Resistant Design and
Construction of Buildings (2nd Revision)
3 IS 13827 1993 Indian Standard Guidelines for Improving Earthquake Resistance of
Earthen Buildings
4 IS 13828 1993 Indian Standard Guidelines for Improving Earthquake Resistance of Low
Strength Masonry Buildings
5 IS 13920 1993 Indian Standard Code of Practice for Ductile Detailing of Reinforced
Concrete Structures Subjected to Seismic Forces
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6 IS 13935 1993 Indian Standard Guidelines for Repair and Seismic Strengthening of
Buildings
The regulations in these standards do not ensure that structures suffer no damage during
earthquake of all magnitudes But to the extent possible they ensure that structures are able to
respond to earthquake shakings of moderate intensities without structural damage and of heavy
intensities without total collapse
IS 1893 (Part I) 2002
IS 1893 is the main code that provides the seismic zone map and specifies seismic design force
This force depends on the mass and seismic coefficient of the structure the latter in turn
depends on properties like seismic zone in which structure lies importance of the structure its
stiffness the soil on which it rests and its ductility For example a building in Bhuj will have
225 times the seismic design force of an identical building in Bombay Similarly the seismic
coefficient for a single-storey building may have 25 times that of a 15-storey building
The revised 2002 edition Part 1 of IS1893 contains provisions that are general in nature and
those applicable for buildings The other four parts of IS 1893 will cover
a) Liquid-Retaining Tanks both elevated and ground supported (Part 2)
b) Bridges and Retaining Walls (Part 3)
c) Industrial Structures including Stack Like Structures (Part 4) and
d) Dams and Embankments (Part 5)
These four documents are under preparation In contrast the 1984 edition of IS1893 had
provisions for all the above structures in a single document
Provisions for Bridges
Seismic design of bridges in India is covered in three codes namely IS 1893 (1984) from the
BIS IRC 6 (2000) from the Indian Roads Congress and Bridge Rules (1964) from the Ministry
of Railways All highway bridges are required to comply with IRC 6 and all railway bridges
with Bridge Rules These three codes are conceptually the same even though there are some
differences in their implementation After the 2001 Bhuj earthquake in 2002 the IRC released
interim provisions that make significant improvements to the IRC6 (2000) seismic provisions
IS 4326 1993 (Reaffirmed 2003)
This code covers general principles for earthquake resistant buildings Selection of materials
and special features of design and construction are dealt with for the following types of
buildings timber constructions masonry constructions using rectangular masonry units and
buildings with prefabricated reinforced concrete roofingflooring elements The code
incorporates Amendment No 3 (January 2005)
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IS 13827 1993 and IS 13828 1993
Guidelines in IS 13827 deal with empirical design and construction aspects for improving
earthquake resistance of earthen houses and those in IS 13828 with general principles of
design and special construction features for improving earthquake resistance of buildings of
low-strength masonry This Masonry includes burnt clay brick or stone masonry in weak
mortars like clay-mud These standards are applicable in seismic zones III IV and V
Constructions based on them are termed non-engineered and are not totally free from collapse
under seismic shaking intensities VIII (MMI) and higher Inclusion of features mentioned in
these guidelines may only enhance the seismic resistance and reduce chances of collapse
IS 13920 1993 (Reaffirmed 2003)
In India reinforced concrete structures are designed and detailed as per the Indian Code IS 456
(2002) However structures located in high seismic regions require ductile design and
detailing Provisions for the ductile detailing of monolithic reinforced concrete frame and shear
wall structures are specified in IS 13920 (1993) After the 2001 Bhuj earthquake this code has
been made mandatory for all structures in zones III IV and V Similar provisions for seismic
design and ductile detailing of steel structures are not yet available in the Indian codes
IS 13935 1993
These guidelines cover general principles of seismic strengthening selection of materials and
techniques for repairseismic strengthening of masonry and wooden buildings The code
provides a brief coverage for individual reinforced concrete members in such buildings but
does not cover reinforced concrete frame or shear wall buildings as a whole Some guidelines
are also laid down for non-structural and architectural components of buildings
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पररलिष Annexure ndash II
Checklist Multiple Choice Questions for Points to be kept in mind during
Construction of Earthquake Resistant Building
S No Description Observer Remarks
1 Seismic Zone in which building is located
i) Zone II ndash Least Seismically Prone Region
ii) Zone III ndash
iii) Zone IV ndash
iv) Zone V ndash Most Seismically Prone Region
Choose Zone
2 Environment condition to which building is exposed
a) Mild b) Moderate c) Severe d) Very Severe e) Extreme
Choose Condition
3 Whether the building is located in Flood Zone YesNo
4 Whether the building is located in Land Slide Zone ie building is on
hill slope or Plane Area
YesNo
5 Type of soil at founding level
a) Rock or Hard Soil
b) Medium Soil
c) Soft Soil
Choose type of soil
6 Type of Building
I) Load Bearing Masonry Building
a) Brick Masonry Construction
b) Stone Masonry construction
II) RCC Framed Structure
a) Regular frame
b) Regular Frame with shear wall
c) Irregular Frame
d) Irregular Frame with shear wall
e) Soft Story Building
Choose type of
building
7 No of Story above Ground Level with provision of Future Extension Mention Storey
8 Category of Building considering Seismic Zone and Importance
Factor (As per Table ndash 102)
i) Category B ndash Building in Seismic Zone II with Importance Factor
10
ii) Category E- Building in Seismic Zone II with Importance Factor
10 and 150
Choose category
9 Bricks should not have compressive strength less than 350 MPa YesNo
10 Minimum wall thickness of brick masonry
i) 1 Brick ndash Single Storey Construction
ii) 1 frac12 Brick ndash In bottom storey up to 3 storey construction amp
1 Brick in top storey with brick masonry
Choose appropriate
11 Height of building is restricted to
i) For A B amp C categories ndash G+2 with flat roof G+1 plus anti for
pitched roof when height of each story not exceed 3 m
ii) D category ndash G+1 with flat Roof
- Ground plus attic for pitched roof
Choose appropriate
12 Max Height of Brick masonry Building ndash 15 m (max 4 storey) YesNo
13 Mortar mix shall be as per Table ndash 102 for category A to E Choose Mortar
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14 Height of Stone Masonry wall
i) For Categories AampB ndash
a) When built in Lime-Sand or Mud mortar
ndash Two storey with flat roof or One Storey plus attic
b) When build in cement sand 16 mortar
- One story higher
ii) For Categories CampD ndash
a) When built in cement Sand 16 Mortar
- Two storey with flat roof or One Storey plus attic for pitched
roof
b) When build in lime sand or Mud mortar
- One story with flat roof or One Story plus attic
Choose appropriate
15 Through stone at full length equal to wall thickness in every 600 mm
lift at not more than 120 m apart horizontally has been provided
YesNo
16 Through stone and Bond Element as per Fig 1024 has been provided YesNo
17 Horizontal Bands
a) Plinth Band
b) Lintel Band
c) Roof Bond
d) Gable Bond
For Over Strengthening Arrangement for Category D amp E Building
have been provided
YesNo
18 Bond shall be made up of Reinforced Concrete of Grade not leaner
than M15 or Reinforced brick work in cement mortar not leaner than
13
YesNo
19 Bond shall be of full width of wall not less than 75 mm in depth and
reinforced with steel as shown in Table ndash 106
YesNo
20 Vertical steel at corners amp junction of wall which are up to 340 mm
(1 frac12 brick) thick shall be provided as shown in Table ndash 101
YesNo
21 General principal for planning building are
i) Building should be as light as possible
ii) All parts of building should be tied together to act as one unit
iii) Projecting part should be avoided
iv) Building having plans with shape L T E and Y shall preferably
be separated in to rectangular parts
v) Structure not to be founded on loose soil which will subside or
liquefy during Earthquake resulting in large differential
settlement
vi) Heavy roofing material should be avoided
vii) Large stair hall shall be separated from Rest of the Building by
means of separation or crumple section
viii) All of the above
ix) None of the above
Choose Correct
22 Structural irregularities may be
i) Horizontal Irregularities
ii) Vertical Irregularities
iii) All of the above
iv) None of the above
Choose Correct
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23 Horizontal Irregularities are
i) Asymmetrical plan shape (eg LTUF)
ii) Horizontal resisting elements (diaphragms)
iii) All of the above
iv) None of the above
Choose Correct
24 Horizontal Irregularities result in
i) Torsion
ii) Diaphragm deformation
iii) Stress Concentration
iv) All of the above
v) None of the above
Choose Correct
25 Vertical Irregularities are
i) Sudden change of stiffness over height of building
ii) Sudden change of strength over height of building
iii) Sudden change of geometry over height of building
iv) Sudden change of mass over height of building
v) All of the above
vi) None of the above
Choose Correct
26 Soft story in one
i) Which has lateral stiffness lt 70 of story above
ii) Which has lateral stiffness lt 80 of average lateral stiffness of 3
storeys above
iii)All of the above
vi) None of the above
Choose Correct
27 Extreme soft storey in one
i) Which has lateral stiffness lt 60 of storey above
ii) Which has lateral stiffness lt 70 of average lateral stiffness of 3
storeys above
iii)All of the above
iv)None of the above
Choose Correct
28 Weak Storey is one
i) Which has lateral strength lt 80 of storey above
ii) Which has lateral strength lt 80 of storey above
iii)All of the above
iv)None of the above
Choose Correct
29 Natural Period of Building
It is the time taken by the building to undergo one complete
cycle of oscillation during shaking
True False
30 Fundamental Natural Period of Building
Natural period with smallest Natural Frequency ie with largest
natural period is called Fundamental Natural Period
True False
31
Type of building frame system
i) Ordinary RC Moment Resisting Frame (OMRF)
ii) Special RC Moment Resisting Frame (SMRF)
iii) Ordinary Shear Wall with OMRF
iv) Ordinary Shear Wall with SMRF
v) Ductile Shear wall with OMRF
vi) Ductile Shear wall with SMRF
vii) All of the above
Choose Correct
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32 Zone factor to be considered for
i) Zone II ndash 010
ii) Zone III ndash 016
iii) Zone IV ndash 024
iv) Zone V ndash 036
True False
33 Importance Factor
i) Important building like school hospital railway station 15
ii) All other buildings 10
True False
34 Design of Earthquake effect is termed as
i) Earthquake Proof Design
or
ii) Earthquake Resistant Design
Choose Correct
35 Seismic Analysis is carried out by
i) Dynamic analysis procedure [Clause 78 of IS1893 (Part I) 2002]
ii) Simplified method referred as Lateral Force Procedure [Clause
75 of IS 1893 (Part I) 2002]
True False
36 Dynamic Analysis is performed for following buildings
(a) Regular Building gt 40 m height in Zone IV amp V
gt 90 height in Zone II amp III
(b) Irregular Building
gt 12 m all framed building in Zone IV amp V
gt 40 m all framed building in Zone II and III
True False
37 Base Shear for Lateral Force Procedure is
VB = Ah W =
True False
38 Distribution of Base Shear to different Floor level is
True False
39 Concept of capacity design is to
Ensure that brittle element will remain elastic at all loads prior to
failure of ductile element
True False
40 lsquoStrong Column ndash Weak Beamrsquo Philosophy is
For a building to remain safe during Earthquake shacking columns
should be stronger than beams and foundation should be stronger
than columns
True False
41 Rigid Diaphragm Action is
Geometric distortion of Slab in horizontal plane under influence of
horizontal Earthquake force is negligible This behaviour is known
as Rigid Diaphragm Action
True False
42 Soft storied buildings are
Column on Ground Storey do not have infill walls (of either
masonry or RC)
True False
43 Soft Storey or Open Ground Story is also termed as weak storey True False
44 Short columns in building suffer significant damage during an earth-
quake
True False
कमटक2017नसईआरबी10
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45 Building can be protected from damage due to Earthquake effect by
using
a) Base Isolation Devices
b) Seismic Dampers
True False
46 Idea behind Base Isolation is
To detach building from Ground so that EQ motion are not
transmitted through the building or at least greatly reduced
True False
47 Base Isolation is done through
Flexible Pads connected to building and foundation True False
48 Seismic Dampers are
(i) Special devices to absorb the energy provided by Ground Motion
to the building
(ii) They act like hydraulic shock absorber in cars
True False
49 Commonly used Seismic Dampers are
(i) Viscous Dampers
(ii) Friction Dampers
(iii) Yielding Dampers
True False
50 For Ductility Requirement
(i) Min Grade of Concrete shall be M20 for all buildings having
more than 3 storeys in height
(ii) Steel Reinforcement of Grade Fe 415 or less only shall be used
(iii) Grade Fe 500 amp Fe 550 having elongation more than 145 may
be used
True False
51 For Ductility Requirement Flexure Members shall satisfy the
following requirement
(i) width of member shall not be less than 200 mm
(ii) width to depth ratio gt 03
(iii) depth of member D lt 14th of clear span
(iv) Factored Axial Stress on the member under Earthquake loading
shall not be greater than 01 fck
True False
52 For Ductility Requirement Longitudinal reinforcement in Flexure
Member shall satisfy the following requirements
i) Top and bottom reinforcement consist of at least 2 bars
throughout member length
ii) Tensile Steel Ratio on any face at any section shall not be less
than ρmin = (024 radic fck) fy
iii) Max Steel ratio on any face at any section shall not exceed
ρmax = 0025
iv) + ve steel at Joint face must be at least equal to half the ndashve steel
at that face
v) Steel provided at each of the top amp bottom face of the member
at any section along its length shall be at least equal to 14th of
max ndashve moment steel provided at the face of either joint
True False
कमटक2017नसईआरबी10
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151
(vi) Detailing of Reinforcement at Beam-Column Joint
(vii) Detailing of Splicing
53 For Ductile Requirement in compression member
i) Minimum diversion of member shall not be less than 200 mm
ii) In Frames with beams cc Span gt 5m or
unsupported length of column gt 4 m shortest dimension shall not
be less than 300 mm
iii) Ratio of shortest cross sectional dimension to the perpendicular
dimension shall probably not less than 04
True False
54 For Ductile Requirement Longitudinal reinforcement in compression
member shall satisfy the following requirements
i) Lap splice shall be provided only in the central half of the member
length proportional as tension splice
ii) Hoop shall be provided over entire splice length at spacing not
greater than 150 mm
iii) Not more than 50 bar shall be spliced at one section
True False
55 When a column terminates into a footing or mat special confining
reinforcement shall extend at least 300 mm into the footing or mat
True False
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152
सोदभयगरोथ सची BIBLIOGRAPHY
1 Guidelines for Earthquake Resistant Non-Engineered Construction reprinted by
Indian Institute of Technology Kanpur 208016 India (Source wwwniceeorg)
2 IS 1893 (Part 1) 2002 Criteria for Earthquake Resistant Design Of Structures
PART- 1 GENERAL PROVISIONS AND BUILDINGS (Fifth Revision )
3
IS 4326 1993 (Reaffirmed 1998) Edition 32 (2002-04) Earthquake Resistant
Design and Construction of Buildings ndash Code of Practice ( Second Revision )
(Incorporating Amendment Nos 1 amp 2)
4 IS 13828 1993 (Reaffirmed 1998) Improving Earthquake Resistance of Low
Strength Masonry Buildings ndash Guidelines
5
IS 13920 1993 (Reaffirmed 1998) Edition 12 (2002-03) Ductile Detailing of
Reinforced Concrete Structures subjected to Seismic Forces ndash Code of Practice
(Incorporating Amendment Nos 1 amp 2)
6 IS 13935 1993 (Reaffirmed 1998) Edition 11 (2002-04) Repair and Seismic
Strengthening of Buildings ndash Guidelines (Incorporating Amendment No 1)
7
Earthquake Tips authored by Prof C V R Murty IIT Kanpur and sponsored by
Building Materials and Technology Promotion Council New Delhi India
(Source www wwwiitkacin)
8
Earthquake Engineering Practice Volume 1 Issue 1 March 2007 published by
National Information Center of Earthquake Engineering IIT Kanpur Kanpur
208016
9 Earthquake Resistant Design of Structures by Pankaj Agarwal and Manish
Shrikhande published by PHI Learning Private Limited Delhi 110092 (2015)
कमटक2017नसईआरबी10
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तटपपणी NOTES
कमटक2017नसईआरबी10
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154
तटपपणी NOTES
कमटक2017नसईआरबी10
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155
हमारा उददशय
अनरकषि परौधौधगकी और कायापरिाली को उननयन करना तथा उतपादकता और
रलव की पररसमपवियो एव िनशजतत क ननषपादन म सधार करना जिसस
अतववाियो म ववशवसनीयता उपयोधगता और दकषता परापत की िा सकA
Our Objective
To upgrade Maintenance Technologies and Methodologies and achieve
improvement in productivity and performance of all Railway assets and
manpower which inter-alia would cover Reliability Availability and
Utilisation
तिसलमर Disclaimer
The document prepared by CAMTECH is meant for the dissemination of the knowledge information
mentioned herein to the field staff of Indian Railways The contents of this handbookbooklet are only for
guidance Most of the data amp information contained herein in the form of numerical values are indicative
and based on codes and teststrials conducted by various agencies generally believed to be reliable While
reasonable care and effort has been taken to ensure that information given is at the time believed to be fare
and correct and opinion based thereupon are reasonable Due to very nature of research it can not be
represented that it is accurate or complete and it should not be relied upon as such The readeruser is
supposed to refer the relevant codes manuals available on the subject before actual implementation in the
field
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156
Hkkjrh jsy jkrdquoV ordf dh thou js[kk ---hellip
INDIAN RAILWAYS Lifeline to the nation hellip
If you have any suggestion amp comments please write to us
Contact person Joint Director (Civil)
Phone (0751) - 2470869
Fax (0751) ndash 2470841
Email dircivilcamtechgmailcom
Charbagh Railway Station Lucknow
पराककथन
दनिया क कई निससो म िाल िी म आए भको पसो ि इमारतसो और जीवि कस काफी िकसाि पहोचाया ि भको प की दनि स दखा जाए तस सबस खतरिाक भवि निमााण
unreinforced ईोट या concrete बलॉक का िसता ि चार मोनजलसो तक क अनिकाोश घरसो कस परबनलत को करीट सलब क साथ burnt clay ईोट नचिाई स निनमात नकया जा रिा ि इसी तरि कई िए चार या पाोच मोनजला घर जस नक छसट और बड शिरसो म परबनलत को करीट फरम स बिाए गए ि म एक उनचत फरम परणाली की कमी रिती ि
िाल िी म आए भको पसो क कारण भारत म इमारतसो और घरसो कस कस सरनित रखा जाय इस पर परमखता स चचाा हई ि भको पीय दशसो म इोजीनियसा कस यि मितवपणा नजममदारी सनिनित करिा ि नक िए निमााण भको प परनतरसिी िसो और यि भी नक उनह मौजदा कमजसर सोरचिाओो दवारा उतपनन समसया का समािाि भी निकालिा ि
यि आशा की जाती ि नक कमटक दवारा तयार पसतिका नसनवल सोरचिाओो क निमााण एवो रखरखाव की गनतनवनियसो म लग भारतीय रलव क इोजीनियररोग कनमायसो क नलए काफी मददगार िसगी
कमटक गवातलयर (ए आर िप) 23 मई 2017 काययकारी तनदशक
FOREWORD
The recent earthquakes occurred in many parts of world has caused considerable damage
to the buildings and lives The most dangerous building construction from an
earthquake point of view is unreinforced brick or concrete block Most houses of upto
four storeys are built of burnt clay brick masonry with reinforced concrete slabs
Similarly many new four or five storey reinforced concrete frame building being
constructed in small and large towns lack a proper frame system
With the recent earthquakes the discussion on how safe buildings and houses are in
India has gained prominence Engineers in seismic countries have the important
responsibility to ensure that the new construction is earthquake resistant and also they
must solve the problem posed by existing weak structures
It is expected that the handbook prepared by CAMTECH will be quite helpful to the
engineering personnel of Indian Railways engaged in construction and maintenance
activities of civil structures
CAMTECHGwalior (AR Tupe)
23 May 2017 Executive Director
भतमका
भारतीय रलव एक बड़ा सगठन ह जिसक पास ससववल इिीननयररग सरचनाओ एव भवनो की ववशाल सपदा मौिद ह भकप की ववनाशकारी परकनत को धयान म रखत हए यह आवशयक ह कक लगभग सभी भवनो चाह व आवासीय ससथागत शकषणिक इतयादद क हो उनकी योिना डििाइन ननमााि तथा रखरखाव भकप परनतरोधी तरीको को अपनाकर ककया िाना चादहए जिसस कक भकप क कारि मानव िीवन व सपवि क नकसान को नयनतम ककया िा सक
ldquoभकप परतिरोधी भवनो क तनरमाणrdquo पर यह हसतपजसतका एक िगह पर पयाापत सामगरी परदान करन का एक परयास ह ताकक वयजतत भवनो क भकप परनतरोधी ननमााि क सलए मलभत ससदधातो को ववकससत कर सही तथा वयवहाररक कायाववधध को अमल म ला सक
इस हसतपजसतका की सामगरी को गयारह अधयायो म ववभाजित ककया गया ह अधयमय-1 पररचय तथा अधयमय-2 भकप इिीननयररग म परयतत शबदावली पररभावित करता ह अधयमय-3 भकप व भकपी खतरो क बार म बननयादी जञान को सकषप म वणिात करता ह अधयमय- 4 भकप पररमाि तथा तीवरता क माप क साथ भारत क भकपीय ज़ोन मानधचतर भकप की ननगरानी क सलए एिससयो क बार म िानकारी परदान करता ह अधयमय-5 व 6 भवन लआउट म भकप परनतरोध क सधार क सलए वयापक ससदधात को बताता ह अधयमय-7 भवन की गनतशील परनतकिया को दशााता ह अधयमय-8 और 9 म कोि पर आधाररत पाशवा बल ननधाारि का तरीका तथा बहमजिला भवन की ldquoितटाइल डिटसलग तथा कपससटी डििाइनrdquo को धयान म रखत हए डििाइन का उदाहरि परसतत ककया गया ह अधयमय-10 म कम शजतत की धचनाई दवारा सरचनाओ क ननमााि को भकप परनतरोधी ससदधातो को धयान म रख वणिात ककया गया ह अधयमय -11 म मौिदा भवनो की भकप परनतरोधी आवशयकताओ को परा करन क सलए भवनो क मौिदा भकपरोधी मलयाकन और पनः सयोिन पर परकाश िाला गया ह
यह हसतपजसतका मखयतः भारतीय रल क फीलि तथा डििाइन कायाालय म कायारत िईएसएसई सतर क सलए ह इस हसतपजसतका को भारतीय रल क ससववल इिीननयसा तथा अनय ववभागो क इिीननयसा दवारा एक सदभा पजसतका क रप म भी इसतमाल ककया िा सकता ह
म शरी एस क ठतकर परोफसर (ररटायिा) आई आई टी रड़की को उनक दवारा ददय गए मागादशान तथा सझावो क सलए अतयनत आभारी ह तथा शरी क सी शातय एसएसईससववल को इस हसतपजसतका क सकलन म उनक समवपात सहयोग क सलए धनयवाद दता ह
यदयवप इस हसतपजसतका को तयार करन म हर तरह की सावधानी बरती गई ह कफर भी कोई तरदट या चक हो तो कपया IRCAMTECHGwalior की िानकारी म लायी िा सकती ह
भारतीय रल क सभी अधधकाररयो और इकाइयो दवारा पसतक की सामगरी म ववसतार तथा सधार क सलए ददय िान वाल सझावो का सवागत ह
कमटक गवातलयर (िी क गपता) 23 मई 2017 सोयकत तनदशकतसतवल
PREFACE
Indian Railways is a big organisation having large assets of Civil Engineering Structures
and Buildings Keeping in mind the destructive nature of Earthquake it is essential that
almost all buildings whether residential institutional educational assembly etc should
be planned designed constructed as well as maintained by adopting Earthquake
Resistant features so that loss due to earthquake to human lives and properties can be
minimised
This handbook on ldquoConstruction of Earthquake Resistant Buildingsrdquo is an attempt to
provide enough material at one place for individual to develop the basic concept for
correctly interpreting and using practices for earthquake resistant construction of
Buildings
Content of this handbook is divided into Eleven Chapters Chapter-1 is Introduction
and Chapter-2 defines Terminology frequently used in Earthquake Engineering
Chapter-3 describes in brief Basic knowledge about Earthquake amp Seismic Hazards
Chapter-4 deals with Measurement of Earthquake magnitude amp intensity with
information about Seismic Zoning Map of India and Agencies for Earthquake
monitoring Chapter-5 amp 6 elaborates General Principle for improving Earthquake
resistance in building layouts Chapter-7 features Dynamic Response of Building In
Chapter-8 amp 9 Codal based procedure for determining lateral loads and Design of
multi-storeyed building with solved example considering Ductile Detailing and Capacity
Design Concept is covered Chapter-10 describes Construction of Low strength
Masonry Structure considering earthquake resistant aspect Chapter-11 enlighten
ldquoSeismic Evaluation amp Retrofittingrdquo for structural upgrading of existing buildings to
meet the seismic requirements
This handbook is primarily written for JESSE level over Indian Railways working in
Field and Design office This handbook can also be used as a reference book by Civil
Engineers and Engineers of other departments of Indian Railways
I sincerely acknowledge the valuable guidance amp suggestion by Shri SK Thakkar
Professor (Retd) IIT Roorkee and also thankful to Shri KC Shakya SSECivil for his
dedicated cooperation in compilation of this handbook
Though every care has been taken in preparing this handbook any error or omission
may please be brought out to the notice of IRCAMTECHGwalior
Suggestion for addition and improvement in the contents from all officers amp units of
Indian Railways are most welcome
CAMTECHGwalior (DK Gupta)
23 May 2017 Joint DirectorCivil
तवषय-सची CONTENT
अधयाय CHAPTER
तववरण DESCRIPTION
पषठ
सोPAGE
NO
पराककथन FOREWORD FROM MEMBER ENGINEERING RLY BOARD पराककथन FOREWORD FROM ADG RDSO पराककथन FOREWORD FROM ED CAMTECH भतमका PREFACE
तवषय-सची CONTENT
सोशोधन पतचययाो CORRECTION SLIPS
1 पररचय Introduction 01
2 भको प इोजीतनयररोग क तलए शबदावली Terminology for Earthquake
Engineering 02-05
3 भको प क बार म About Earthquake 06-16
31 भको प Earthquake 06
32 नकि कारणसो स िसता ि भको प What causes Earthquake 06
33 नववतानिक गनतनवनि Tectonic Activity 06
34 नववतानिक पलट का नसदाोत Theory of Plate Tectonics 07
35 लचीला ररबाउोड नसदाोत Elastic Rebound Theory 11
36 भको प और दसष क परकार Types of Earthquakes and Faults 11
37 जमीि कस निलती ि How the Ground shakes 12
38 भको प या भको पी खतरसो का परभाव Effects of Earthquake or Seismic
Hazards 13
4 भको पी जोन और भको प का मापन Seismic Zone and Measurement
of Earthquake 17-28
41 भको पी जसि Seismic Zone 17
42 भको प का मापि Measurement of Earthquake 19
43 भको प पररमाण सकल क परकार Types of Earthquake Magnitude
Scales 20
44 भको प तीवरता Earthquake Intensity 22
45 भको प निगरािी और सवाओो क नलए एजनसयसो Agencies for Earthquake
Monitoring and Services 28
5 भवन म भको प परतिरोध म सधार क तलए सामानय तसदाोि General
Principle for improving Earthquake Resistance in Building 29-33
51 िलकापि Lightness 29
52 निमााण की निरोतरता Continuity of Construction 29
53 परसजसतटोग एवो ससपडड पाटटास Projecting and Suspended Parts 29
54 भवि की आकनत Shape of Building 29
55 सनविा जिक नबसतडोग लआउट Preferred Building Layouts 30
56 नवनभनन नदशाओो म शसति Strength in Various Directions 30
57 िी ोव Foundations 30
58 छत एवो मोनजल Roofs and Floors 30
59 सीनियाो Staircases 31
510 बॉकस परकार निमााण Box Type Construction 33
511 अनि सरिा Fire Safety 33
6
भको प क दौरान आर सी भवनो ो क परदशयन पर सटरकचरल अतनयतमििाओो
का परभाव Effect of Structural Irregularities on Performance of
RC Buildings during Earthquakes
34-38
61 सटर कचरल अनियनमतताओो का परभाव Effect of Structural Irregularities 34
62 िनतज अनियनमतताएो Horizontal Irregularities 34
63 ऊरधाािर अनियनमतताएो Vertical Irregularities 36
64
भवि नवनयास अनियनमतताएो ndash समसयाए ववशलिि एव ननदान क उपाय Building Irregularities ndash Problems Analysis and Remedial
Measures 37
7 भवन की िायनातमक तवशषिाएा Dynamic Characteristics of
Building 39-47
71 डायिानमक नवशषताए Dynamic Characteristics 39
72 पराकनतक अवनि Natural Period 39
73 पराकनतक आवनि Natural Frequency 39
74 पराकनतक अवनि कस परभानवत करि वाल कारक Factors influencing
Natural Period 40
75 Mode आकनत Mode Shape 42
76 Mode आकनतयसो कस परभानवत करि वाल कारक Factors influencing
Mode Shapes 44
77 सोरचिा की परनतनकरया Response of Structure 46
78 नडजाइि सपटर म Design Spectrum 46
8 तिजाइन पारशय बलो ो क तनधायरण क तलए कोि आधाररि िरीका Code
Based Procedure for Determination of Design Lateral Loads 48-59
81 भको पी नडजाइि की नफलससफ़ी Philosophy of Seismic Design 48
82 भको पी नवशलषण क नलए तरीक Methods for Seismic Analysis 48
83 डायिानमक नवशलषण Dynamic Analysis 49
84 पारशा बल परनकरया Lateral Force Procedure 49
85 को पि की मौनलक पराकनतक अवनि Fundamental Natural Period of
Vibration 52
86 नडजाइि पारशा बल Design Lateral Force 53
87 नडजाइि बल का नवतरण Distribution of Design Force 53
88 नडजाइि उदािरण Design Example ndash To determine Base Shear and
its distribution along Height of Building 54
9 ढााचागि सोरचना का तनमायण Construction of Framed Structure 60-90
91
गरतवाकषाण लसनडोग और भको प लसनडोग म आर सी नबसतडोग का वयविार Behaviour of RC Building in Gravity Loading and Earthquake
Loading 60
92 परबनलत को करीट इमारतसो पर िनतज भको प का परभाव Effect of Horizontal
Earthquake Force on RC Buildings 61
93 िमता नडजाइि सोकलपिा Capacity Design Concept 61
94 लचीलापि और ऊजाा का अपवयय Ductility and Energy Dissipation 62
95 lsquoमजबतिोभ ndash कमजसर बीमrsquo फलससफ़ी lsquoStrong Column ndash Weak
Beamrsquo Philosophy 62
96 कठसर डायाफराम नकरया Rigid Diaphragm Action 63
97
सॉफट सटसरी नबसतडोग क साथ ndash ओपि गराउोड सटसरी नबसतडोग जस नक भको प क
समय कमजसर िसती ि Building with Soft storey ndash Open Ground
Storey Building that is vulnerable in Earthquake 63
98 भको प क दौराि लघ कॉलम वाली इमारतसो का वयविार Behavior of
Buildings with Short Columns during Earthquakes 65
99 भको प परनतरसिी इमारतसो की लचीलापि आवशयकताए Ductility
requirements of Earthquake Resistant Buildings 66
910
बीम नजनह आर सी इमारतसो म भको प बलसो का नवरसि करि क नलए डाला जाता
ि Beams that are required to resist Earthquake Forces in RC
Buildings 66
911 फलकसचरल ममबसा क नलए सामानय आवशयकताए General Requirements
for Flexural Members 68
912
कॉलम नजनह आर सी इमारतसो म भको प बलसो का नवरसि करि क नलए डाला
जाता ि Columns that are required to resist Earthquake Forces in
RC Buildings 69
913 एकसीयल लसडड मबसा क नलए सामानय आवशयकताए General
Requirements for Axial Loaded Members 71
914 बीम-कॉलम जसड जस आर सी भविसो म भको प बलसो का नवरसि करत ि Beam-
Column Joints that resist Earthquakes Forces in RC Buildings 72
915 नवशष सीनमत सदढीकरण Special Confining Reinforcement 74
916
नवशषतः भको पीय ितर म कतरिी दीवारसो वाली इमारतसो का निमााण Construction of Buildings with Shear Walls preferably in Seismic
Regions 75
917 इमपरवड नडजाइि रणिीनतयाो Improved design strategies 76
918 नडजाइि उदािरण Design Example ndash Beam Design of RC Frame
with Ductile Detailing 78
10 अलप सामरथय तचनाई सोरचनाओो क तनमायण Construction of Low
Strength Masonry Structures 91-106
101 भको प क दौराि ईोट नचिाई की दीवारसो का वयविार Behaviour of
Brick Masonry Walls during Earthquakes 91
102 नचिाई वाली इमारतसो म बॉकस एकशि कस सनिनित कर How to ensure
Box Action in Masonry Buildings 92
103 िनतज बड की भनमका Role of Horizontal Bands 93
104 अिसलोब सदढीकरण Vertical Reinforcement 95
105 दीवारसो म सराखसो का सोरिण Protection of Openings in Walls 96
106
भको प परनतरसिी ईोट नचिाई भवि क निमााण ित सामानय नसदाोत General
Principles for Construction of Earthquake Resistant Brick
Masonry Building
97
107 ओपनिोग का परभाव Influence of Openings 100
108 िारक दीवारसो म ओपनिोग परदाि करि की सामानय आवशयकताए General Requirements of Providing Openings in Bearing Walls
100
109 भको पी सदिीकरण वयवसथा Seismic Strengthening Arrangements 101
1010 भको प क दौराि सटसि नचिाई की दीवारसो का वयविार Behaviour of Stone
Masonry Walls during Earthquakes 104
1011
भकप परनतरोधी सटोन धचनाई क ननमााि हत सामानय ससदधात General
Principles for Construction of Earthquake Resistant Stone
Masonry Building
104
11 भकपीय रलयमकन और रटरोफिट ग Seismic Evaluation and
Retrofitting 107-142
111 भकपीय मलयाकन Seismic Evaluation 107
112 भवनो की रटरोकिदटग Retrofitting of Building 116
113
आरसी भवनो क घटको म सामानय भकपी कषनतया और उनक उपचार Common seismic damage in components of RC
Buildings and their remedies 133
114 धचनाई सरचनाओ की रटरोकिदटग Retrofitting of Masonry
Structures 141
Annex ndash I भारिीय भको पी सोतििाएा Indian Seismic Codes 143-145
Annex ndash II Checklist Multiple Choice Questions for Points to be kept in
mind during Construction of Earthquake Resistant Building 146-151
सोदभयगरोथ सची BIBLIOGRAPHY 152
तटपपणी NOTES 153-154
हमारा उददशय एव डिसकलरर OUR OBJECTIVE AND DISCLAIMER
सोशसिि पनचायसो का परकाशि
ISSUE OF CORRECTION SLIPS
इस ििपसतिका क नलए भनवषय म परकानशत िसि वाली सोशसिि पनचायसो कस निमनािसार सोखाोनकत
नकया जाएगा
The correction slips to be issued in future for this handbook will be numbered as
follows
कमटक2017नसईआरबी10सीएस XX नदिाोक_____________________
CAMTECH2017CERB10CS XX date_________________________
जिा xx सोबसतित सोशसिि पची की करम सोखा ि (01 स परारमभ िसकर आग की ओर)
Where ldquoXXrdquo is the serial number of the concerned correction slip (starting
from 01 onwards)
परकातशि सोशोधन पतचययाा W a
CORRECTION SLIPS ISSUED
करसो Sr No
परकाशन
तदनाोक Date of
issue
सोशोतधि पषठ सोखया िथा मद सोखया Page no and Item No modified
तटपपणी Remarks
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1
अधयाय Chapter ndash 1
पररचय Introduction
To avoid a great earthquake disaster with its severe consequences special consideration must be
given Engineers in seismic countries have the important responsibility to ensure that the new
construction is earthquake resistant and also they must solve the problem posed by existing weak
structures
Most of the loss of life in past earthquakes has occurred due to the collapse of buildings
constructed with traditional materials like stone brick adobe (kachcha house) and wood which
were not particularly engineered to be earthquake resistant In view of the continued use of such
buildings it is essential to introduce earthquake resistance features in their construction
The problem of earthquake engineering can be divided into two parts first to design new
structures to perform satisfactorily during an earthquake and second to retrofit existing structures
so as to reduce the loss of life during an earthquake Every city in the world has a significant
proportion of existing unsafe buildings which will produce a disaster in the event of a strong
ground shaking Engineers have the responsibility to develop appropriate methods of retrofit
which can be applied when the occasion arises
The design of new building to withstand ground shaking is prime responsibility of engineers and
much progress has been made during the past 40 years Many advances have been made such as
the design of ductile reinforced concrete members Methods of base isolation and methods of
increasing the damping in structures are now being utilized for important buildings both new and
existing Improvements in seismic design are continuing to be made such as permitting safe
inelastic deformations in the event of very strong ground shaking
A problem that the engineer must share with the seismologistgeologist is that of prediction of
future occurrence of earthquake which is not possible in current scenario
Earthquake resistant construction requires seismic considerations at all stages from architectural
planning to structural design to actual constructions and quality control
Problems pertaining to Earthquake engineering in a seismic country cannot be solved in a short
time so engineers must be prepared to continue working to improve public safety during
earthquake In time they must control the performance of structures so that effect of earthquake
does not create panic in society and its after effects are easily restorable
To ensure seismic resistant construction earthquake engineering knowledge needs to spread to a
broad spectrum of professional engineers within the country rather than confining it to a few
organizations or individuals as if it were a super-speciality
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2
अधयाय Chapter ndash 2
भको प इोजीतनयररोग क तलए शबदावली Terminology for Earthquake Engineering
21 फोकस या िाइपोसटर Focus or Hypocenter
In an earthquake the waves emanate from a finite area
of rocks However the point from which the waves
first emanate or where the fault movement starts is
called the earthquake focus or hypocenter
22 इपीसटर Epicentre
The point on the ground surface just above the focus is called the epicentre
23 सििी फोकस भको प Shallow Focus Earthquake
Shallow focus earthquake occurs where the focus is less than 70 km deep from ground surface
24 इोटरमीतिएट फोकस भको प Intermediate Focus Earthquake
Intermediate focus earthquake occurs where the focus is between 70 km to 300 km deep
25 गिरा फोकस भको प Deep Focus Earthquake
Deep focus earthquake occurs where the depth of focus is more than 300 km
26 इपीसटर दरी Epicentre Distance
Distance between epicentre and recording station in km or in degrees is called epicentre distance
27 पवय क झटक Foreshocks
Fore shocks are smaller earthquakes that precede the main earthquake
28 बाद क झटक Aftershocks
Aftershocks are smaller earthquakes that follow the main earthquake
29 पररमाण Magnitude
The magnitude of earthquake is a number which is a measure of energy released in an
earthquake It is defined as logarithm to the base 10 of the maximum trace amplitude expressed
in microns which the standard short-period torsion seismometer (with a period of 08s
Fig 21Basic terminology
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magnification 2800 and damping nearly critical) would register due to the earthquake at an
epicentral distance of 100 km
210 िीवरिा Intensity
The intensity of an earthquake at a place is a measure of the strength of shaking during the
earthquake and is indicated by a number according to the modified Mercalli Scale or MSK
Scale of seismic intensities
211 पररमाण और िीवरिा क बीच बतनयादी फकय Basic difference between Magnitude and
Intensity
Magnitude of an earthquake is a measure of its size
whereas intensity is an indicator of the severity of
shaking generated at a given location Clearly the
severity of shaking is much higher near the
epicenter than farther away
This can be elaborated by considering the analogy
of an electric bulb Here the size of the bulb (100-
Watt) is like the magnitude of an earthquake (M)
and the illumination (measured in lumens) at a
location like the intensity of shaking at that location
(Fig 22)
212 दरवण Liquefaction
Liquefaction is a state in saturated cohesion-less soil wherein the effective shear strength is
reduced to negligible value for all engineering purpose due to pore pressure caused by vibrations
during an earthquake when they approach the total confining pressure In this condition the soil
tends to behave like a fluid mass
213 तववियतनक लकषण Tectonic Feature
The nature of geological formation of the bedrock in the earthrsquos crust revealing regions
characterized by structural features such as dislocation distortion faults folding thrusts
volcanoes with their age of formation which are directly involved in the earth movement or
quake resulting in the above consequences
214 भको पी दरवयमान Seismic Mass
It is the seismic weight divided by acceleration due to gravity
215 भको पी भार Seismic Weight
It is the total dead load plus appropriate amounts of specified imposed load
Fig 22 Reducing illumination with distance
from an electric bulb
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216 आधार Base
It is the level at which inertia forces generated in the structure are transferred to the foundation
which then transfers these forces to the ground
217 दरवयमान का क दर Centre of Mass
The point through which the resultant of the masses of a system acts is called Centre of Mass
This point corresponds to the centre of gravity of masses of system
218 कठोरिा का क दर Centre of Stiffness
The point through which the resultant of the restoring forces of a system acts is called Centre of
stiffness
219 बॉकस परणाली Box System
Box is a bearing wall structure without a space frame where the horizontal forces are resisted by
the walls acting as shear walls
220 पटटा Band
A reinforced concrete reinforced brick or wooden runner provided horizontally in the walls to tie
them together and to impart horizontal bending strength in them
221 लचीलापन Ductility
Ductility of a structure or its members is the capacity to undergo large inelastic deformations
without significant loss of strength or stiffness
222 किरनी दीवार Shear Wall
Shear wall is a wall that is primarily designed to resist lateral forces in its own plane
223 िनय का बयौरा Ductile Detailing
Ductile Detailing is the preferred choice of location and amount of reinforcement in reinforced
concrete structures to provide adequate ductility In steel structures it is the design of members
and their connections to make them adequate ductile
224 लचीला भको पी तवरण गणाोक Elastic Seismic Acceleration Co-Efficient A
This is the horizontal acceleration value as a fraction of acceleration due to gravity versus
natural period of vibration T that shall be used in design of structures
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225 पराकतिक अवतध Natural Period T
Natural period of a structure is its time period of undamped vibration
a) Fundamental Natural Period Tl It is the highest modal time period of vibration along the
considered direction of earthquake motion
b) Modal Natural Period Tk Modal natural period of mode k is the time period of vibration in
mode k
226 नॉमयल मोि Normal Mode
Mode of vibration at which all the masses in a structure attain maximum values of displacements
and rotations and also pass through equilibrium positions simultaneously
227 ओवरसटरगथ Overstrength
Strength considering all factors that may cause its increase eg steel strength being higher than
the specified characteristic strength effect of strain hardening in steel with large strains and
concrete strength being higher than specified characteristic value
228 ररसाोस कमी कारक Response Reduction Factor R
The factor by which the actual lateral force that would be generated if the structure were to
remain elastic during the most severe shaking that is likely at that site shall be reduced to obtain
the design lateral force
229 ररसाोस सकटर म Response Spectrum
The representation of the maximum response of idealized single degree freedom system having
certain period and damping during that earthquake The maximum response is plotted against the
undamped natural period and for various damping values and can be expressed in terms of
maximum absolute acceleration maximum relative velocity or maximum relative displacement
230 तमटटी परोफ़ाइल फकटर Soil Profile Factor S
A factor used to obtain the elastic acceleration spectrum depending on the soil profile below the
foundation of structure
कमटक2017नसईआरबी10
CAMTECH2017CERB10
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6
अधयाय Chapter ndash 3
भको प क बार म About Earthquake
31 भको प Earthquake
Vibrations of earthrsquos surface caused by waves coming from a source of disturbance inside the
earth are described as earthquakes
Earthquake is a natural phenomenon occurring with all uncertainties
During the earthquake ground motions occur in a random fashion both horizontally and
vertically in all directions radiating from epicentre
These cause structures to vibrate and induce inertia forces on them
32 तकन कारणो ो स िोिा ि भको प What causes Earthquake
Earthquakes may be caused by
Tectonic activity
Volcanic activity
Land-slides and rock-falls
Rock bursting in a mine
Nuclear explosions
33 तववियतनक गतितवतध Tectonic Activity
Tectonic activity pertains to geological formation of the bedrock in the earthrsquos crust characterized
by structural features such as dislocation distortion faults folding thrusts volcanoes directly
involved in the earth movement
As engineers we are interested in earthquakes that are large enough and close enough (to the
structure) to cause concern for structural safety- usually caused by tectonic activity
Earth (Fig 31) consists of following segments ndash
solid inner core (radius ~1290km) that consists of heavy
metals (eg nickel and iron)
liquid outer core(thickness ~2200km)
stiffer mantle(thickness ~2900km) that has ability to flow
and
crust(thickness ~5 to 40km) that consists of light
materials (eg basalts and granites)
At the Core the temperature is estimated to be ~2500degC the
pressure ~4 million atmospheres and density ~135 gmcc
this is in contrast to ~25degC 1 atmosphere and 15 gmcc on the surface of the Earth
Fig 31 Inside the Earth
कमटक2017नसईआरबी10
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7
Due to prevailing high temperature and pressure gradients between the Crust and the Core the
local convective currents in mantle (Fig 32) are developed These convection currents result in a
circulation of the earthrsquos mass hot molten lava comes out and the cold rock mass goes into the
Earth The mass absorbed eventually melts under high temperature and pressure and becomes a
part of the Mantle only to come out again from another location
Near the bottom of the crust horizontal component currents impose shear stresses on bottom of
crust causing movement of plates on earthrsquos surface The movement causes the plates to move
apart in some places and to converge in others
34 तववियतनक पलट का तसदाोि Theory of Plate Tectonics
Tectonic Plates Basic hypothesis of plate tectonics is that the earthrsquos surface consists of a
number of large intact blocks called plates or tectonic plates and these plates move with respect
to each other due to the convective flows of Mantle material which causes the Crust and some
portion of the Mantle to slide on the hot molten outer core The major plates are shown in
Fig 33
The earthrsquos crust is divided into six continental-sized plates (African American Antarctic
Australia-Indian Eurasian and Pacific) and about 14 of sub-continental size (eg Carribean
Cocos Nazca Philippine etc) Smaller platelets or micro-plates also have broken off from the
larger plates in the vicinity of many of the major plate boundaries
Fig 32 Convention current in mantle
कमटक2017नसईआरबी10
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8
Fig 33 The major tectonic plates mid-oceanic ridges trenches and transform faults of
the earth Arrows indicate the directions of plate movement
कमटक2017नसईआरबी10
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9
The relative deformation between plates occurs only in narrow zones near their boundaries
These deformations are
1 Aseismic deformation This deformation of the plates occurs slowly and continuously
2 Seismic deformation This deformation occurs with sudden outburst of energy in the form of
earthquakes
The boundaries are (i) Convergent (ii) Divergent (iii) Transform
Convergent boundary Sometimes the plate in the front is slower Then the plate behind it
comes and collides (and mountains are formed) This type of inter-plate interaction is the
convergent boundary (Fig 34)
Divergent boundary Sometimes two plates move away from one another (and rifts are
created) This type of inter-plate interaction is the divergent boundary (Fig 35)
Transform boundary Sometimes two plates move side-by-side along the same direction or in
opposite directions This type of inter-plate interaction is the transform boundary (Fig 36)
Since the deformation occurs predominantly at the boundaries between the plates it would be
expected that the locations of earthquakes would be concentrated near plate boundaries The map
of earthquake epicentres shown in Fig 37 provides strong support to confirm the theory of plate
tectonics The dots represent the epicentres of significant earthquakes It is apparent that the
locations of the great majority of earthquakes correspond to the boundaries between plates
Fig 34 Convergent Boundary
Fig 35 Divergent Boundary
Fig 36 Transform Boundary
कमटक2017नसईआरबी10
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Fig 37 Worldwide seismic activity
कमटक2017नसईआरबी10
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35 लचीला ररबाउोि तसदाोि Elastic Rebound Theory
Earth crust for some reason is moving in opposite
directions on certain faults This sets up elastic
strains in the rocks in the region near this fault As
the motion goes on the stresses build up in the
rocks until the stresses are large enough to cause
slip between the two adjoining portions of rocks
on either side A rupture takes place and the
strained rock rebounds back due to internal stress
Thus the strain energy in the rock is relieved
partly or fully (Fig 38)
Fault The interface between the plates where the movement has taken place is called fault
Slip When the rocky material along the interface of the plates in the Earthrsquos Crust reaches its
strength it fractures and a sudden movement called slip takes place
The sudden slip at the fault causes the earthquake A violent shaking of the Earth during
which large elastic strain energy released spreads out in the form of seismic waves that travel
through the body and along the surface of the
Earth
After elastic rebound there is a readjustment and
reapportion of the remaining strains in the region
The stress grows on a section of fault until slip
occurs again this causes yet another even though
smaller earthquake which is termed as aftershock
The aftershock activity continues until the
stresses are below the threshold level everywhere
in the rock
After the earthquake is over the process of strain build-up at this modified interface between the
tectonic plates starts all over again This is known as the Elastic Rebound Theory (Fig 39)
36 भको प और दोष क परकार Types of Earthquakes and Faults
Inter-plate Earthquakes Most earthquakes occurring along the boundaries of the tectonic
plates are called Inter-plate Earthquakes (eg 1897
Assam (India) earthquake)
Intra-plate Earthquakes Numbers of earthquakes
occurring within the plate itself but away from the
plate boundaries are called Intra-plate Earthquakes
(eg 1993 Latur (India) earthquake)
Note In both types of earthquakes the slip
generated at the fault during earthquakes is along
Fig 310 Type of Faults
Fig 38 Elastic Strain Build-Up and Brittle Rupture
Fig 39 Elastic Rebound Theory
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both vertical and horizontal directions (called Dip Slip) and lateral directions (called Strike
Slip) with one of them dominating sometimes (Fig 310)
37 जमीन कस तिलिी ि How the Ground shakes
Seismic waves Large strain energy released during an earthquake travels as seismic waves in all
directions through the Earthrsquos layers reflecting and refracting at each interface (Fig 311)
There are of two types of waves 1) Body Waves
2) Surface Waves
Body waves are of two types
a) Primary Waves (P-Wave)
b) Secondary Wave (S-Wave)
Surface waves are of two types namely
a) Love Waves
b) Rayleigh Waves
Body Waves Body waves have spherical wave front They consist of
Primary Waves (P-waves) Under P-waves [Fig 311(a)] material particles undergo
extensional and compressional strains along direction of energy transmission These waves
are faster than all other types of waves
Secondary Waves (S-waves) Under S-waves [Fig 311(b)] material particles oscillate at
Fig 311 Arrival of Seismic Waves at a Site
Fig 311(a) Motions caused by Primary Waves
Fig 311(b) Motions caused by Secondary Waves
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right angles to direction of energy transmission This type of wave shears the rock particle to
the direction of wave travel Since the liquid has no shearing resistance these waves cannot
pass through liquids
Surface Waves Surface waves have cylindrical wave front They consist of
Love Waves In case of Love waves [Fig 311(c)] the displacement is transverse with no
vertical or longitudinal components (ie similar to secondary waves with no vertical
component) Particle motion is restricted to near the surface Love waves being transverse
waves these cannot travel in liquids
Rayleigh Waves Rayleigh waves [Fig 311(d)] make a material particle oscillate in an
elliptic path in the vertical plane with horizontal motion along direction of energy
transmission
Note Primary waves are fastest followed in sequence by Secondary Love and Rayleigh waves
38 भको प या भको पी खिरो ो का परभाव Effects of Earthquake or Seismic Hazards
Basic causes of earthquake-induced damage are
Ground shaking
Structural hazards
Liquefaction
Ground failure Landslides
Tsunamis and
Fire
Fig 311(c) Motions caused by Love Waves
Fig 311(d) Motions caused by Rayleigh Waves
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381 जमीन को पन Ground shaking
Ground shaking can be considered to be the most important of all seismic hazards because all
the other hazards are caused by ground shaking
When an earthquake occurs seismic waves radiate away from the source and travel rapidly
through the earthrsquos crust
When these waves reach the ground surface they produce shaking that may last from seconds
to minutes
The strength and duration of shaking at a particular site depends on the size and location of
the earthquake and on the characteristics of the site
At sites near the source of a large earthquake ground shaking can cause tremendous damage
Where ground shaking levels are low the other seismic hazards may be low or nonexistent
Strong ground shaking can produce extensive damage from a variety of seismic hazards
depending upon the characteristics of the soil
The characteristics of the soil can greatly influence the nature of shaking at the ground
surface
Soil deposits tend to act as ldquofiltersrdquo to seismic waves by attenuating motion at certain
frequencies and amplifying it at others
Since soil conditions often vary dramatically over short distances levels of ground shaking
can vary significantly within a small area
One of the most important aspects of geotechnical earthquake engineering practice involves
evaluation of the effects of local soil conditions on strong ground motion
382 सोरचनातमक खिर Structural Hazards
Without doubt the most dramatic and memorable images of earthquake damage are those of
structural collapse which is the leading cause of death and economic loss in many
earthquakes
As the earth vibrates all buildings on the ground surface will respond to that vibration in
varying degrees
Earthquake induced accelerations velocities and displacements can damage or destroy a
building unless it has been designed and constructed or strengthened to be earthquake
resistant
The effect of ground shaking on buildings is a principal area of consideration in the design of
earthquake resistant buildings
Seismic design loads are extremely difficult to determine due to the random nature of
earthquake motions
Structures need not collapse to cause death and damage Falling objects such as brick facings
and parapets on the outside of a structure or heavy pictures and shelves within a structure
have caused casualties in many earthquakes Interior facilities such as piping lighting and
storage systems can also be damaged during earthquakes
However experiences from past strong earthquakes have shown that reasonable and prudent
practices can keep a building safe during an earthquake
Over the years considerable advancement in earthquake-resistant design has moved from an
emphasis on structural strength to emphases on both strength and ductility In current design
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practice the geotechnical earthquake engineer is often consulted for providing the structural
engineer with appropriate design ground motions
383 दरवीकरण Liquefaction
In some cases earthquake damage have occurred when soil deposits have lost their strength and
appeared to flow as fluids This phenomenon is termed as liquefaction In liquefaction the
strength of the soil is reduced often drastically to the point where it is unable to support
structures or remain stable Because it only occurs in saturated soils liquefaction is most
commonly observed near rives bays and other bodies of water
Soil liquefaction can occur in low density saturated sands of relatively uniform size The
phenomenon of liquefaction is particularly important for dams bridges underground pipelines
and buildings standing on such ground
384 जमीन तवफलिा लि सलाइि Ground Failure Land slides
1) Earthquake-induced ground Failure has been observed in the form of ground rupture along
the fault zone landslides settlement and soil liquefaction
2) Ground rupture along a fault zone may be very limited or may extend over hundreds of
kilometers
3) Ground displacement along the fault may be horizontal vertical or both and can be
measured in centimetres or even metres
4) A building directly astride such a rupture will be severely damaged or collapsed
5) Strong earthquakes often cause landslides
6) In a number of unfortunate cases earthquake-induced landslides have buried entire towns
and villages
7) Earthquake-induced landslides cause damage by destroying buildings or disrupting bridges
and other constructed facilities
8) Many earthquake-induced landslides result from liquefaction phenomenon
9) Others landslides simply represent the failures of slopes that were marginally stable under
static conditions
10) Landslide can destroy a building the settlement may only damage the building
385 सनामी Tsunamis
1) Tsunamis or seismic sea waves are generally produced by a sudden movement of the ocean
floor
2) Rapid vertical seafloor movements caused by fault rupture during earthquakes can produce
long-period sea waves ie Tsunamis
3) In the open sea tsunamis travel great distances at high speeds but are difficult to detect ndash
they usually have heights of less than 1 m and wavelengths (the distance between crests) of
several hundred kilometres
4) As a tsunami approaches shore the decreasing water depth causes its speed to decrease and
the height of the wave to increase
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5) As the water waves approach land their velocity decreases and their height increases from
5 to 8 m or even more
6) In some coastal areas the shape of the seafloor may amplify the wave producing a nearly
vertical wall of water that rushes far inland and causes devastating damage
7) Tsunamis can be devastating for buildings built in coastal areas
386 अति Fire
When the fire following an earthquake starts it becomes difficult to extinguish it since a strong
earthquake is accompanied by the loss of water supply and traffic jams Therefore the
earthquake damage increases with the earthquake-induced fire in addition to the damage to
buildings directly due to earthquakes
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अधयाय Chapter ndash 4
भको पी जोन और भको प का मापन Seismic Zone and Measurement of Earthquake
41 भको पी जोन Seismic Zone
Due to convective flow of mantle material crust of Earth and some portion of mantle slide on hot
molten outer core This sliding of Earthrsquos mass takes place in pieces called Tectonic Plates The
surface of the Earth consists of seven major tectonic plates (Fig 41)
They are
1 Eurasian Plate
2 Indo-Australian Plate
3 Pacific Plate
4 North American Plate
5 South American Plate
6 African Plate
7 Antarctic Plate
India lies at the northwestern end of the Indo Australian Plate (Fig 42) This Plate is colliding
against the huge Eurasian Plate and going under the Eurasian Plate Three chief tectonic sub-
regions of India are
the mighty Himalayas along the north
the plains of the Ganges and other rivers and
the peninsula
Most earthquakes occur along the Himalayan plate boundary (these are inter-plate earthquakes)
but a number of earthquakes have also occurred in the peninsular region (these are intra-plate
earthquakes)
Fig 41 Major Tectonic Plates on the Earthrsquos surface
Fig 42 Geographical Layout and Tectonic Plate
Boundaries in India
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Bureau of Indian Standards [IS1893 (part ndash 1) 2002] based on various scientific inputs from a
number of agencies including earthquake data supplied by Indian Meteorological Department
(IMD) has grouped the country into four seismic zones viz Zone II III IV and V Of these
Zone V is rated as the most seismically prone region while Zone II is the least (Fig 43)
Indian Seismic code (IS 18932002) divides the country into four seismic zones based on the
expected intensity of shaking in future earthquake The four zones correspond to areas that have
potential for shaking intensity on MSK scale as shown in the table
Seismic Zone Intensity on MSK scale of total area
II (Low intensity zone) VI (or less) 43
III (Moderate intensity zone) VII 27
IV (Severe intensity zone) VIII 18
V (Very Severe intensity zone) IX (and above) 12
Fig 43 Map showing Seismic Zones of India [IS 1893 (Part 1) 2002]
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42 भको प का मापन Measurement of Earthquake
421 मापन उपकरण Measuring Instruments
Seismograph The instrument that measures earthquake shaking is known as a seismograph
(Fig 44) It has three components ndash
Sensor ndash It consists of pendulum mass
string magnet and support
Recorder ndash It consists of drum pen and
chart paper
Timer ndash It consists of the motor that rotates
the drum at constant speed
Seismoscopes Some instruments that do not
have a timer device provide only the maximum
extent (or scope) of motion during the
earthquake
Digital instruments The digital instruments using modern computer technology records the
ground motion on the memory of the microprocessor that is in-built in the instrument
Note The analogue instruments have evolved over time but today digital instruments are more
commonly used
422 मापन क सकल Scale of Measurement
The Richter Magnitude Scale (also called Richter scale) assigns a magnitude number to quantify
the energy released by an earthquake Richter scale is a base 10 logarithmic scale which defines
magnitude as the logarithm of the ratio of the amplitude of the seismic wave to an arbitrary minor
amplitude
The magnitude M of an Earthquake is defined as
M = log10 A - log10 A0
Where
A = Recorded trace amplitude for that earthquake at a given distance as written by a
standard type of instrument (say Wood Anderson instrument)
A0 = Same as A but for a particular earthquake selected as standard
This number M is thus independent of distance between the epicentre and the station and is a
characteristic of the earthquake The standard shock has been defined such that it is low enough
to make the magnitude of most of the recorded earthquakes positive and is assigned a magnitude
of zero Thus if A = A0
Fig 44 Schematic of Early Seismograph
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M = log10 A0 - log10 A0 = 0
Standard shock of magnitude zero It is defined as one that records peak amplitude of one
thousandths of a millimetre at a distance of 100 km from the epicentre
1) Zero magnitude does not mean that there is no earthquake
2) Magnitude of an earthquake can be a negative number also
3) An earthquake that records peak amplitude of 1 mm on a standard seismograph at 100 km
will have its magnitude as
M = log10 (1) - log10 (10-3
)= 0 ndash (-3) = 3
Magnitude of a local earthquake It is defined as the logarithm to base 10 of the maximum
seismic wave amplitude (in thousandths of a mm) recorded on Wood Anderson seismograph at a
distance of 100 kms from the earthquake epicentre
1) With increase in magnitude by 10 the energy released by an earthquake increases by a
factor of about 316
2) A magnitude 80 earthquake releases about 316 times the energy released by a magnitude
70 earthquake or about 1000 times the energy released by a 60 earthquake
3) With increase in magnitude by 02 the energy released by the earthquake doubles
43 भको प पररमाण सकल क परकार Types of Earthquake Magnitude Scales
Several scales have historically been described as the ldquoRitcher Scalerdquo The Ritcher local
magnitude (ML) is the best known magnitude scale but it is not always the most appropriate scale
for description of earthquake size The Ritcher local magnitude does not distinguish between
different types of waves
At large epicentral distances body waves have usually been attenuated and scattered sufficiently
that the resulting motion is dominated by surface waves
Other magnitude scales that base the magnitude on the amplitude of a particular wave have been
developed They are
a) Surface Wave Magnitude (MS)
b) Body Wave Magnitude (Mb)
c) Moment Magnitude (Mw)
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431 सिि लिर पररमाण Surface Wave Magnitude (MS)
The surface wave magnitude (Gutenberg and Ritcher 1936) is a worldwide magnitude scale
based on the amplitude of Rayleigh waves with period of about 20 sec The surface wave
magnitude is obtained from
MS = log A + 166 log Δ + 20
Where A is the maximum ground displacement in micrometers and Δ is the epicentral distance of
the seismometer measured in degrees (3600 corresponding to the circumference of the earth)
The surface wave magnitude is most commonly used to describe the size of shallow (less than
about 70 km focal depth) distant (farther than about 1000 km) moderate to large earthquakes
432 बॉिी लिर पररमाण Body Wave Magnitude (Mb)
For deep-focus earthquakes surface waves are often too small to permit reliable evaluation of the
surface wave magnitude The body wave magnitude (Gutenberg 1945) is a worldwide magnitude
scale based on the amplitude of the first few cycles of p-waves which are not strongly influenced
by the focal depth (Bolt 1989) The body wave magnitude can be expressed as
Mb = log A ndash log T + 001Δ + 59
Where A is the p-wave amplitude in micrometers and T is the period of the p-wave (usually
about one sec)
Saturation
For strong earthquakes the measured
ground-shaking characteristics become
less sensitive to the size of the
earthquake than the smaller earthquakes
This phenomenon is referred to as
saturation (Fig 45)
The body wave and the Ritcher local
magnitudes saturate at magnitudes of 6
to 7 and the surface wave magnitude
saturates at about Ms = 8
To describe the size of a very large
earthquake a magnitude scale that does
not depend on ground-shaking levels
and consequently does not saturate
would be desirable
Fig 45 Saturation of various magnitude scale Mw (Moment
Magnitude) ML (Ritcher Local Magnitude) MS (Surface Wave
Magnitude) mb (Short-period Body Wave Magnitude) mB
(Long-period Body Wave Magnitude) and MJMA (Japanese
Meteorological Agency Magnitude)
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433 पल पररमाण Moment Magnitude (Mw)
The only magnitude scale that is not subject to saturation is the moment magnitude
The moment magnitude is given by
Mw = [(log M0)15] ndash 107
Where M0 is the seismic moment in dyne-cm
44 भको प िीवरिा Earthquake Intensity
Earthquake magnitude is simply a measure of the size of the earthquake reflecting the elastic
energy released by the earthquake It is usually referred by a certain real number on the Ritcher
scale (eg magnitude 65 earthquake)
On the other hand earthquake intensity indicates the extent of shaking experienced at a given
location due to a particular earthquake It is usually referred by a Roman numeral on the
Modified Mercalli Intensity (MMI) scale as given below
I Not felt except by a very few under especially favourable circumstances
II Felt by only a few persons at rest especially on upper floors of buildings delicately
suspended objects may swing
III Felt quite noticeably indoors especially on upper floors of buildings but many people
do not recognize it as an earthquake standing motor cars may rock slightly vibration
like passing of truck duration estimated
IV During the day felt indoors by many outdoors by few at night some awakened
dishes windows doors disturbed walls make cracking sound sensation like heavy
truck striking building standing motor cars rocked noticeably
V Felt by nearly everyone many awakened some dishes windows etc broken a few
instances of cracked plaster unstable objects overturned disturbances of trees piles
and other tall objects sometimes noticed pendulum clocks may stop
VI Felt by all many frightened and run outdoors some heavy furniture moved a few
instances of fallen plaster or damaged chimneys damage slight
VII Everybody runs outdoors damage negligible in buildings of good design and
construction slight to moderate in well-built ordinary structures considerable in
poorly built or badly designed structures some chimneys broken noticed by persons
driving motor cars
VIII Damage slight in specially designed structures considerable in ordinary substantial
buildings with partial collapse great in poorly built structures panel walls thrown out
of frame structures fall of chimneys factory stacks columns monuments walls
heavy furniture overturned sand and mud ejected in small amounts changes in well
water persons driving motor cars disturbed
IX Damage considerable in specially designed structures well-designed frame structures
thrown out of plumb great in substantial buildings with partial collapse buildings
shifted off foundations ground cracked conspicuously underground pipes broken
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X Some well-built wooden structures destroyed most masonry and frame structures
destroyed with foundations ground badly cracked rails bent landslides considerable
from river banks and steep slopes shifted sand and mud water splashed over banks
XI Few if any (masonry) structures remain standing bridges destroyed broad fissures in
ground underground pipelines completely out of service earth slumps and land slips
in soft ground rails bent greatly
XII Damage total practically all works of construction are damaged greatly or destroyed
waves seen on ground surface lines of sight and level are destroyed objects thrown
into air
441 MSK िीवरिा सकल MSK Intensity Scale
The MSK intensity scale is quite comparable to the Modified Mercalli intensity scale but is more
convenient for application in field and is widely used in India In assigning the MSK intensity
scale at a site due attention is paid to
Type of Structures (Table ndash A)
Percentage of damage to each type of structure (Table ndash B)
Grade of damage to different types of structures (Table ndash C)
Details of Intensity Scale (Table ndash D)
The main features of MSK intensity scale are as follows
Table ndash A Types of Structures (Buildings)
Type of
Structures
Definitions
A Building in field-stone rural structures unburnt ndash brick houses clay houses
B Ordinary brick buildings buildings of large block and prefabricated type half
timbered structures buildings in natural hewn stone
C Reinforced buildings well built wooden structures
Table ndash B Definition of Quantity
Quantity Percentage
Single few About 5 percent
Many About 50 percent
Most About 75 percent
Table ndash C Classification of Damage to Buildings
Grade Definitions Descriptions
G1 Slight damage Fine cracks in plaster fall of small pieces of plaster
G2 Moderate damage Small cracks in plaster fall of fairly large pieces of plaster
pantiles slip off cracks in chimneys parts of chimney fall down
G3 Heavy damage Large and deep cracks in plaster fall of chimneys
G4 Destruction Gaps in walls parts of buildings may collapse separate parts of
the buildings lose their cohesion and inner walls collapse
G5 Total damage Total collapse of the buildings
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Table ndash D Details of Intensity Scale
Intensity Descriptions
I Not noticeable The intensity of the vibration is below the limits of sensibility
the tremor is detected and recorded by seismograph only
II Scarcely noticeable
(very slight)
Vibration is felt only by individual people at rest in houses
especially on upper floors of buildings
III Weak partially
observed only
The earthquake is felt indoors by a few people outdoors only in
favourable circumstances The vibration is like that due to the
passing of a light truck Attentive observers notice a slight
swinging of hanging objects somewhat more heavily on upper
floors
IV Largely observed The earthquake is felt indoors by many people outdoors by few
Here and there people awake but no one is frightened The
vibration is like that due to the passing of a heavily loaded truck
Windows doors and dishes rattle Floors and walls crack
Furniture begins to shake Hanging objects swing slightly Liquid
in open vessels are slightly disturbed In standing motor cars the
shock is noticeable
V Awakening
a) The earthquake is felt indoors by all outdoors by many Many
people awake A few run outdoors Animals become uneasy
Buildings tremble throughout Hanging objects swing
considerably Pictures knock against walls or swing out of
place Occasionally pendulum clocks stop Unstable objects
overturn or shift Open doors and windows are thrust open
and slam back again Liquids spill in small amounts from
well-filled open containers The sensation of vibration is like
that due to heavy objects falling inside the buildings
b) Slight damages in buildings of Type A are possible
c) Sometimes changes in flow of springs
VI Frightening
a) Felt by most indoors and outdoors Many people in buildings
are frightened and run outdoors A few persons loose their
balance Domestic animals run out of their stalls In few
instances dishes and glassware may break and books fall
down Heavy furniture may possibly move and small steeple
bells may ring
b) Damage of Grade 1 is sustained in single buildings of Type B
and in many of Type A Damage in few buildings of Type A
is of Grade 2
c) In few cases cracks up to widths of 1cm possible in wet
ground in mountains occasional landslips change in flow of
springs and in level of well water are observed
VII Damage of buildings
a) Most people are frightened and run outdoors Many find it
difficult to stand The vibration is noticed by persons driving
motor cars Large bells ring
b) In many buildings of Type C damage of Grade 1 is caused in
many buildings of Type B damage is of Grade 2 Most
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buildings of Type A suffer damage of Grade 3 few of Grade
4 In single instances landslides of roadway on steep slopes
crack inroads seams of pipelines damaged cracks in stone
walls
c) Waves are formed on water and is made turbid by mud stirred
up Water levels in wells change and the flow of springs
changes Sometimes dry springs have their flow resorted and
existing springs stop flowing In isolated instances parts of
sand and gravelly banks slip off
VIII Destruction of
buildings
a) Fright and panic also persons driving motor cars are
disturbed Here and there branches of trees break off Even
heavy furniture moves and partly overturns Hanging lamps
are damaged in part
b) Most buildings of Type C suffer damage of Grade 2 and few
of Grade 3 Most buildings of Type B suffer damage of Grade
3 Most buildings of Type A suffer damage of Grade 4
Occasional breaking of pipe seams Memorials and
monuments move and twist Tombstones overturn Stone
walls collapse
c) Small landslips in hollows and on banked roads on steep
slopes cracks in ground up to widths of several centimetres
Water in lakes becomes turbid New reservoirs come into
existence Dry wells refill and existing wells become dry In
many cases change in flow and level of water is observed
IX General damage of
buildings
a) General panic considerable damage to furniture Animals run
to and fro in confusion and cry
b) Many buildings of Type C suffer damage of Grade 3 and a
few of Grade 4 Many buildings of Type B show a damage of
Grade 4 and a few of Grade 5 Many buildings of Type A
suffer damage of Grade 5 Monuments and columns fall
Considerable damage to reservoirs underground pipes partly
broken In individual cases railway lines are bent and
roadway damaged
c) On flat land overflow of water sand and mud is often
observed Ground cracks to widths of up to 10 cm on slopes
and river banks more than 10 cm Furthermore a large
number of slight cracks in ground falls of rock many
landslides and earth flows large waves in water Dry wells
renew their flow and existing wells dry up
X General destruction of
building
a) Many buildings of Type C suffer damage of Grade 4 and a
few of Grade 5 Many buildings of Type B show damage of
Grade 5 Most of Type A have destruction of Grade 5
Critical damage to dykes and dams Severe damage to
bridges Railway lines are bent slightly Underground pipes
are bent or broken Road paving and asphalt show waves
b) In ground cracks up to widths of several centimetres
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sometimes up to 1m Parallel to water courses occur broad
fissures Loose ground slides from steep slopes From river
banks and steep coasts considerable landslides are possible
In coastal areas displacement of sand and mud change of
water level in wells water from canals lakes rivers etc
thrown on land New lakes occur
XI Destruction
a) Severe damage even to well built buildings bridges water
dams and railway lines Highways become useless
Underground pipes destroyed
b) Ground considerably distorted by broad cracks and fissures
as well as movement in horizontal and vertical directions
Numerous landslips and falls of rocks The intensity of the
earthquake requires to be investigated specifically
XII Landscape changes
a) Practically all structures above and below ground are greatly
damaged or destroyed
b) The surface of the ground is radically changed Considerable
ground cracks with extensive vertical and horizontal
movements are observed Falling of rock and slumping of
river banks over wide areas lakes are dammed waterfalls
appear and rivers are deflected The intensity of the
earthquake requires to be investigated specially
442 तवतभनन सकलो ो की िीवरिा मलो ो की िलना Comparison of Intensity Values of
Different Scales
443 तवतभनन पररमाण और िीवरिा क भको प का परभाव Effect of Earthquake of various
Magnitude and Intensity
The following describes the typical effects of earthquakes of various magnitudes near the
epicenter The values are typical only They should be taken with extreme caution since intensity
and thus ground effects depend not only on the magnitude but also on the distance to the
epicenter the depth of the earthquakes focus beneath the epicenter the location of the epicenter
and geological conditions (certain terrains can amplify seismic signals)
Fig 45 Comparison of Intensity Values of Different Scales
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Magnitude Description Mercalli
intensity
Average earthquake effects Average
frequency of
occurrence
(estimated)
10-19 Micro I Micro earthquakes not felt or felt rarely
Recorded by seismographs
Continualseveral
million per year
20-29 Minor I to II Felt slightly by some people No damage to
buildings
Over one million
per year
30-39 III to IV Often felt by people but very rarely causes
damage Shaking of indoor objects can be
noticeable
Over 100000 per
year
40-49 Light IV to VI Noticeable shaking of indoor objects and
rattling noises Felt by most people in the
affected area Slightly felt outside
Generally causes none to minimal damage
Moderate to significant damage very
unlikely Some objects may fall off shelves
or be knocked over
10000 to 15000
per year
50-59 Moderate VI to
VIII
Can cause damage of varying severity to
poorly constructed buildings At most none
to slight damage to all other buildings Felt
by everyone
1000 to 1500 per
year
60-69 Strong VII to X Damage to a moderate number of well-built
structures in populated areas Earthquake-
resistant structures survive with slight to
moderate damage Poorly designed
structures receive moderate to severe
damage Felt in wider areas up to hundreds
of mileskilometers from the epicenter
Strong to violent shaking in epicentral area
100 to 150 per
year
70-79 Major VIII or
Greater
Causes damage to most buildings some to
partially or completely collapse or receive
severe damage Well-designed structures
are likely to receive damage Felt across
great distances with major damage mostly
limited to 250 km from epicenter
10 to 20 per year
80-89 Great Major damage to buildings structures
likely to be destroyed Will cause moderate
to heavy damage to sturdy or earthquake-
resistant buildings Damaging in large
areas Felt in extremely large regions
One per year
90 and
greater
At or near total destruction ndash severe damage
or collapse to all buildings Heavy damage
and shaking extends to distant locations
Permanent changes in ground topography
One per 10 to 50
years
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45 भको प तनगरानी और सवाओो क तलए एजतसयो ो Agencies for Earthquake Monitoring and
Services
Centre for Seismology (CS) in Indian Meteorological Department (IMD) under Ministry of
Earth Sciences is nodal agency of Government of India dealing with various activities in
the field of seismology and allied disciplines and is responsible for monitoring seismic
activity in and around the country
The major activities currently being pursued by the Centre for Seismology (CS) include
a) Earthquake monitoring on 24X7 basis including real time seismic monitoring for early
warning of tsunamis
b) Operation and maintenance of national seismological network and local networks
c) Seismological data centre and information services
d) Seismic hazard and risk related studies
e) Field studies for aftershock swarm monitoring site response studies
f) Earthquake processes and modelling etc
These activities are being managed by various unitsgroups of the Centre for Seismology
(CS) as detailed below
1) Centre for Seismology (CS) is maintaining a country wide National Seismological
Network (NSN) consisting of a total of 82 seismological stations spread over the
entire length and breadth of the country This includes
a) 16-station V-SAT based digital seismic telemetry system around National Capital
Territory (NCT) of Delhi
b) 20-station VSAT based real time seismic monitoring network in North East region
of the country
(c) 17-station Real Time Seismic Monitoring Network (RTSMN) to monitor and
report large magnitude under-sea earthquakes capable of generating tsunamis on
the Indian coastal regions
2) The remaining stations are of standalone analog type
3) A Control Room is in operation on a 24X7 basis at premises of IMD Headquarters in
New Delhi with state-of-the art facilities for data collection processing and
dissemination of information to the concerned user agencies
4) India represented by CSIMD is a permanent Member of the International
Seismological Centre (ISC) UK
5) Seismological Bulletins of CSIMD are shared regularly with International
Seismological Centre (ISC) UK for incorporation in the ISCs Monthly Seismological
Bulletins which contain information on earthquakes occurring all across the globe
6) Towards early warning of tsunamis real-time continuous seismic waveform data of
three IMD stations viz Portblair Minicoy and Shillong is shared with global
community through IRIS (Incorporated Research Institutions of Seismology)
Washington DC USA
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अधयाय Chapter ndash 5
भवन म भको प परतिरोध म सधार क तलए सामानय तसदाोि General Principle for improving Earthquake Resistance in Building
51 िलकापन Lightness
Since the earthquake force is a function of mass the building should be as light as possible
consistent with structural safety and functional requirements Roofs and upper storeys of
buildings in particular should be designed as light as possible
52 तनमायण की तनरोिरिा Continuity of Construction
As far as possible all parts of the building should be tied together in such a manner that
the building acts as one unit
For integral action of building roof and floor slabs should be continuous throughout as
far as possible
Additions and alterations to the structures should be accompanied by the provision of
positive measures to establish continuity between the existing and the new construction
53 परोजककटोग एवो ससिि पाटटयस Projecting and Suspended Parts
Projecting parts should be avoided as far as possible If the projecting parts cannot be
avoided they should be properly reinforced and firmly tied to the main structure
Ceiling plaster should preferably be avoided When it is unavoidable the plaster should
be as thin as possible
Suspended ceiling should be avoided as far as possible Where provided they should be
light and adequately framed and secured
54 भवन की आकति Shape of Building
In order to minimize torsion and stress concentration the building should have a simple
rectangular plan
It should be symmetrical both with respect to mass and rigidity so that the centre of mass
and rigidity of the building coincide with each other
It will be desirable to use separate blocks of rectangular shape particularly in seismic
zones V and IV
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55 सतवधा जनक तबकडोग लआउट Preferred Building Layouts
Buildings having plans with shapes like L T E and Y shall preferably be separated into
rectangular parts by providing separation sections at appropriate places Typical examples are
shown in Fig 51
56 तवतभनन तदशाओो म शककत Strength in Various Directions
The structure shall have adequate strength against earthquake effects along both the horizontal
axes considering the reversible nature of earthquake forces
57 नी ोव Foundations
For the design of foundations the provisions of IS 1904 1986 in conjunctions with IS
1893 1984 shall generally be followed
The sub-grade below the entire area of the building shall preferably be of the same type of
the soil Wherever this is not possible a suitably located separation or crumple section shall
be provided
Loose fine sand soft silt and expansive clays should be avoided If unavoidable the
building shall rest either on a rigid raft foundation or on piles taken to a firm stratum
However for light constructions the following measures may be taken to improve the soil
on which the foundation of the building may rest
a) Sand piling and b) Soil stabilization
Structure shall not be founded on loose soil which will subside or liquefy during an
earthquake resulting in large differential settlement
58 छि एवो मोतजल Roofs and Floors
581 सपाट छि या फशय Flat roof or floor
Flat roof or floor shall not preferably be made of terrace of ordinary bricks supported on steel
timber or reinforced concrete joists nor they shall be of a type which in the event of an
earthquake is likely to be loosened and parts of all of which may fall If this type of construction
cannot be avoided the joists should be blocked at ends and bridged at intervals such that their
spacing is not altered during an earthquake
Fig 51 Typical Shapes of Building with Separation Sections [IS 4326 1993]
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582 ढलान वाली छि Pitched Roofs
For pitched roofs corrugated iron or asbestos sheets should be used in preference to
country Allahabad or Mangalore tiles or other loose roofing units
All roofing materials shall be properly tied to the supporting members
Heavy roofing materials should generally be avoided
583 सोवि छि Pent Roofs
All roof trusses should be supported on and fixed to timber band reinforced concrete band or
reinforced brick band The holding down bolts should have adequate length as required for
earthquake and wind forces
Where a trussed roof adjoins a masonry gable the ends of the purlins should be carried on and
secured to a plate or bearer which should be adequately bolted to timber reinforced concrete or
reinforced brick band at the top of gable end masonry
- At tie level all the trusses and the gable end should be provided with diagonal braces in plan
so as to transmit the lateral shear due to earthquake force to the gable walls acting as shear
walls at the ends
NOTE ndash Hipped roof in general have shown better structural behaviour during earthquakes than gable
ended roofs
584 जक मिराब Jack Arches
Jack arched roofs or floors where used should be provided with mild steel ties in all spans along
with diagonal braces in plan to ensure diaphragm actions
59 सीतढ़याो Staircases
The interconnection of the stairs with the adjacent floors should be appropriately treated by
providing sliding joints at the stairs to eliminate their bracing effect on the floors
Ladders may be made fixed at one end and freely resting at the other
Large stair halls shall preferably be separated from rest of the building by means of
separation or crumple section
Three types of stair construction may be adopted as described below
591 अलग सीतढ़याो Separated Staircases
One end of the staircase rests on a wall and the other end is carried by columns and beams which
have no connection with the floors The opening at the vertical joints between the floor and the
staircase may be covered either with a tread plate attached to one side of the joint and sliding on
the other side or covered with some appropriate material which could crumple or fracture during
an earthquake without causing structural damage
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The supporting members columns or walls are
isolated from the surrounding floors by means of
separation or crumple sections A typical
example is shown in Fig 52
592 तबलट-इन सीतढ़याो Built-in Staircase
When stairs are built monolithically with floors they can be protected against damage by
providing rigid walls at the stair opening An arrangement in which the staircase is enclosed by
two walls is given in Fig 53 (a) In such cases the joints as mentioned in respect of separated
staircases will not be necessary
The two walls mentioned above enclosing the staircase shall extend through the entire height of
the stairs and to the building foundations
Fig 53 (a) Rigidly Built-In Staircase [IS 4326 1993]
Fig 52 Separated Staircase
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593 सलाइतिोग जोड़ो ो वाली सीतढ़याो Staircases with Sliding Joints
In case it is not possible to provide rigid walls around stair openings for built-in staircase or to
adopt the separated staircases the staircases shall have sliding joints so that they will not act as
diagonal bracing (Fig 53 (b))
510 बॉकस परकार तनमायण Box Type Construction
This type of construction consists of prefabricated or in-situ masonry wall along with both the
axes of the building The walls support vertical loads and also act as shear walls for horizontal
loads acting in any direction All traditional masonry construction falls under this category In
prefabricated wall construction attention should be paid to the connections between wall panels
so that transfer of shear between them is ensured
511 अति सरकषा Fire Safety
Fire frequently follows an earthquake and therefore buildings should be constructed to make
them fire resistant in accordance with the provisions of relevant Indian Standards for fire safety
The relevant Indian Standards are IS 1641 1988 IS 1642 1989 IS 1643 1988 IS 1644 1988
and IS 1646 1986
Fig 53 (b) Staircase with Sliding Joint
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अधयाय Chapter ndash 6
भको प क दौरान आर सी भवनो ो क परदशयन पर सटरकचरल अतनयतमििाओो का परभाव Effect of Structural Irregularities on Performance of RC Buildings during Earthquakes
61 सटरकचरल अतनयतमििाओो का परभाव Effect of Structural Irregularities
There are numerous examples of past earthquakes in which the cause of failure of reinforced
concrete building has been ascribed to irregularities in configurations
Irregularities are mainly categorized as
(i) Horizontal Irregularities
(ii) Vertical Irregularities
62 कषतिज अतनयतमििाएो Horizontal Irregularities
Horizontal irregularities refer to asymmetrical plan shapes (eg L- T- U- F-) or discontinuities
in the horizontal resisting elements (diaphragms) such as cut-outs large openings re-entrant
corners and other abrupt changes resulting in torsion diaphragm deformations stress
concentration
Table ndash 61 Definitions of Irregular Buildings ndash Plan Irregularities (Fig 61)
S
No
Irregularity Type and Description
(i) Torsion Irregularity To be considered when floor diaphragms are rigid in their own
plan in relation to the vertical structural elements that resist the lateral forces Torsional
irregularity to be considered to exist when the maximum storey drift computed with
design eccentricity at one end of the structures transverse to an axis is more than 12
times the average of the storey drifts at the two ends of the structure
Fig 61 (a)
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(ii) Re-entrant Corners Plan configurations of a structure and its lateral force resisting
system contain re-entrant corners where both projections of the structure beyond the re-
entrant corner are greater than 15 percent of its plan dimension in the given direction
Fig 61 (b)
(iii) Diaphragm Discontinuity Diaphragms with abrupt discontinuities or variations in
stiffness including those having cut-out or open areas greater than 50 percent of the
gross enclosed diaphragm area or changes in effective diaphragm stiffness of more than
50 percent from one storey to the next
Fig 61 (c)
(iv) Out-of-Plane Offsets Discontinuities in a lateral force resistance path such as out-of-
plane offsets of vertical elements
Fig 61 (d)
(v) Non-parallel Systems The vertical elements
resisting the lateral force are not parallel to or
symmetric about the major orthogonal axes or the
lateral force resisting elements
Fig 61 (e)
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63 ऊरधायधर अतनयतमििाएो Vertical Irregularities
Vertical irregularities referring to sudden change of strength stiffness geometry and mass result
in irregular distribution of forces and or deformation over the height of building
Table ndash 62 Definition of Irregular Buildings ndash Vertical Irregularities (Fig 62)
S
No
Irregularity Type and Description
(i) a) Stiffness Irregularity ndash Soft Storey A soft storey is one in which the lateral stiffness is
less than 70 percent of that in the storey above or less than 80 percent of the average lateral
stiffness of the three storeys above
b) Stiffness Irregularity ndash Extreme Soft Storey A extreme soft storey is one in which the
lateral stiffness is less than 60 percent of that in the storey above or less than 70 percent of
the average stiffness of the three storeys above For example buildings on STILTS will fall
under this category
Fig 62 (a)
(ii) Mass Irregularity Mass irregularity shall be considered to exist where the seismic weight
of any storey is more than 200percent of that of its adjacent storeys The irregularity need
not be considered in case of roofs
Fig 62 (b)
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(iii) Vertical Geometric Irregularity Vertical geometric irregularity shall be considered to
exist where the horizontal dimension of the lateral force resisting system in any storey is
more than150 percent of that in its adjacent storey
Fig 62 (c)
(iv) In-Plane Discontinuity in Vertical Elements Resisting Lateral Force A in-plane offset of
the lateral force resisting elements greater than the length of those elements
Fig 62 (d)
(v) Discontinuity in Capacity ndash Weak Storey A weak storey is one in which the storey lateral
strength is less than 80 percent of that in the storey above The storey lateral strength is the
total strength of all seismic force resisting elements sharing the storey shear in the
considered direction
64 भवन तवनयास अतनयतमििाएो ndash सरसकयमए ववशलषण एव तनदमन क उपमय Building
Irregularities ndash Problems Analysis and Remedial Measures
The influence of irregularity on performance of building during earthquakes is presented to
account for the effects of these irregularities in analysis of problems and their solutions along
with the design
Vertical Geometric Irregularity when L2gt15 L1
In-Plane Discontinuity in Vertical Elements Resisting Weak Storey when Filt08Fi+ 1
Lateral Force when b gta
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Architectural problems Structural problems Remedial measures
Extreme heightdepth ratio
High overturning forces large drift causing non-structural damage foundation stability
Revive properties or special structural system
Extreme plan area Built-up large diaphragm forces Subdivide building by seismic joints
Extreme length depth ratio
Built-up of large lateral forces in perimeter large differences in resistance of two axes Experience greater variations in ground movement and soil conditions
Subdivide building by seismic joints
Variation in perimeter strength-stiffness
Torsion caused by extreme variation in strength and stiffness
Add frames and disconnect walls or use frames and lightweight walls
False symmetry Torsion caused by stiff asymmetric core Disconnect core or use frame with non-structural core walls
Re-entrant corners Torsion stress concentrations at the notches
Separate walls uniform box centre box architectural relief diagonal reinforcement
Mass eccentricities Torsion stress concentrations Reprogram or add resistance around mass to balance resistance and mass
Vertical setbacks and reverse setbacks
Stress concentration at notch different periods for different parts of building high diaphragm forces to transfer at setback
Special structural systems careful dynamic analysis
Soft storey frame Causes abrupt changes of stiffness at point of discontinuity
Add bracing add columns braced
Variation in column stiffness
Causes abrupt changes of stiffness much higher forces in stiffer columns
Redesign structural system to balance stiffness
Discontinuous shear wall Results in discontinuities in load path and stress concentration for most heavily loaded elements
Primary concern over the strength of lower level columns and connecting beams that support the load of discontinuous frame
Weak column ndash strong beam
Column failure occurs before beam short column must try and accommodate storey height displacement
Add full walls to reduce column forces or detach spandrels from columns or use light weight curtain wall with frame
Modification of primary structure
Most serious when masonry in-fill modifies structural concept creation of short stiff columns result in stress concentration
Detach in-fill or use light-weight materials
Building separation (Pounding)
Possibility of pounding dependent on building period height drift distance
Ensure adequate separation assuming opposite building vibrations
Coupled Incompatible deformation between walls and links
Design adequate link
Random Openings Seriously degrade capacity at point of maximum force transfer
Careful designing adequate space for reinforcing design
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अधयाय Chapter ndash 7
भवन की िायनातमक तवशषिाएा Dynamic Characteristics of Building
71 िायनातमक तवशषिाएा Dynamic Characteristics
Buildings oscillate during earthquake shaking The oscillation causes inertia force to be induced
in the building The intensity and duration of oscillation and the amount of inertia force induced
in a building depend on features of buildings called dynamic characteristics of building
The important dynamic characteristics of buildings are
a) Modes of Oscillation
b) Damping
A mode of oscillation of a building is defined by associated Natural Period and Deformed Shape
in which it oscillates Every building has a number of natural frequencies at which it offers
minimum resistance to shaking induced by external effects (like earthquakes and wind) and
internal effects(like motors fixed on it) Each of these natural frequencies and the associated
deformation shape of a building constitute a Natural Mode of Oscillation
The mode of oscillation with the smallest natural frequency (and largest natural period) is called
the Fundamental Mode the associated natural period T1is called the Fundamental Natural
Period
72 पराकतिक अवतध Natural Period
Natural Period (Tn) of a building is the time taken by it to undergo one complete cycle of
oscillation It is an inherent property of a building controlled by its mass m and stiffness k These
three quantities are related by
Its unit is second (s)
73 पराकतिक आवततत Natural Frequency
The reciprocal (1Tn) of natural period of a building is called the Natural Frequency fn its unit is
Hertz (Hz)
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74 पराकतिक अवतध को परभातवि करन वाल कारक Factors influencing Natural Period
741 कठोरिा का परभाव Effect of Stiffness Stiffer buildings have smaller natural period
742 दरवयमान का परभाव Effect of Mass Heavier buildings have larger natural period
743 कॉलम अतभतवनयास का परभाव Effect of Column Orientation Buildings with larger
column dimension oriented in the direction reduces the translational natural period of oscillation
in that direction
Fig 72 Effect of Mass
Fig 71 Effect of Stiffness
Fig 73 Effect of Column Orientation
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744 भवन की ऊो चाई का परभाव Effect of Building Height Taller buildings have larger
natural period
745 Unreinforced तचनाई भराव का परभाव Effect of Unreinforced Masonry Infills Natural
Period of building is lower when the stiffness contribution of URM infill is considered
Fig 75 Effect of Building Height
Fig 74 Effect of Building Height
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75 Mode आकति Mode Shape
Mode shape of oscillation associated with a natural period of a building is the deformed shape of
the building when shaken at the natural period Hence a building has as many mode shapes as
the number of natural periods
The deformed shape of the building associated with oscillation at fundamental natural period is
termed its first mode shape Similarly the deformed shapes associated with oscillations at
second third and other higher natural periods are called second mode shape third mode shape
and so on respectively
Fundamental Mode Shape of Oscillation
As shown in Fig 76 there are three basic modes of oscillation namely
1 Pure translational along X-direction
2 Pure translational along Y-direction and
3 Pure rotation about Z-axis
Regular buildings
These buildings have pure mode shapesThe Basic modes of oscillation ie two translational and
one rotational mode shapes
Irregular buildings
These buildings that have irregular geometry non-uniform distribution of mass and stiffness in
plan and along the height have mode shapes which are a mixture of these pure mode shapes
Each of these mode shapes is independent implying it cannot be obtained by combining any or
all of the other mode shapes
a) Fundamental and two higher translational modes of oscillation along X-direction of a
five storey benchmark building First modes shape has one zero crossing of the un-deformed
position second two and third three
Fig 76 Basic modes of oscillation
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b) Diagonal modes of oscillation First three modes of oscillation of a building symmetric in
both directions in plan first and second are diagonal translational modes and third rotational
c) Effect of modes of oscillation on column bending Columns are severely damaged while
bending about their diagonal direction
Fig 77 Fundamental and two higher translational modes of oscillation
along X-direction of a five storey benchmark building
Fig 78 Diagonal modes of oscillation
Fig 79 Effect of modes of oscillation on column bending
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76 Mode आकतियो ो को परभातवि करन वाल कारक Factors influencing Mode Shapes
761 Effect of relative flexural stiffness of structural elements Fundamental translational
mode shape changes from flexural-type to shear-type with increase in beam flexural stiffness
relative to that of column
762 Effect of axial stiffness of vertical members Fundamental translational mode shape
changes from flexure-type to shear-type with increase in axial stiffness of vertical members
Fig 710 Effect of relative flexural stiffness of structural elements
Fig 711 Effect of axial stiffness of vertical members
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763 Effect of degree of fixity at member ends Lack of fixity at beam ends induces flexural-
type behaviour while the same at column bases induces shear-type behaviour to the fundamental
translational mode of oscillation
Fig 712 Effect of degree of fixity at member ends
764 Effect of building height Fundamental translational mode shape of oscillation does not
change significantly with increase in building height unlike the fundamental translational natural
period which does change
Fig 713 Effect of building height
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765 Influence of URM Infill Walls in Mode Shape of RC frame Buildings Mode shape of
a building obtained considering stiffness contribution of URM is significantly different from that
obtained without considering the same
77 सोरचना की परतितकरया Response of Structure
The earthquakes cause vibratory motion which is cyclic about the equilibrium The structural
response is vibratory (Dynamic) and it is cyclic about the equilibrium position of structure The
fundamental natural frequency of most civil engineering structures lie in the range of 01 sec to
30 sec or so This is also the range of frequency content of earthquake-generated ground
motions Hence the ground motion imparts considerable amount of energy to the structures
Initially the structure responds elastically to the ground motion however as its yield capacity is
exceeded the structure responds in an inelastic manner During the inelastic response stiffness
and energy dissipation properties of the structure are modified
Response of the structure to a given strong ground motion depends not only on the properties of
input ground motion but also on the structural properties
78 तिजाइन सकटर म Design Spectrum
The design spectrum is a design specification which is arrived at by considering all aspects The
design spectrum may be in terms of acceleration velocity or displacement
Fig 714 Influence of URM Infill Walls in Mode Shape of RC frame Buildings
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47
Since design spectrum is a specification for design it cannot be viewed in isolation without
considering the other factors that go into the design process One must concurrently specify
a) The procedure to calculate natural period of the structure
b) The damping to be used for a given type of structure
c) The permissible stresses and strains load factors etc
Unless this information is part of a design spectrum the design specification is incomplete
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48
अधयाय Chapter ndash 8
डिजमइन पमशवा बलो क तनधमारण क ललए कोि आधमररि िरीकम Code based Procedure for Determination of Design Lateral Loads
81 भको पी तिजाइन की तफलोसफ़ी Philosophy of Seismic Design
Design of earthquake effect is not termed as Earthquake Proof Design Actual forces that appear
on structure during earthquake are much greater than the design forces Complete protection
against earthquake of all size is not economically feasible and design based alone on strength
criteria is not justified Earthquake demand is estimated only based on concept of probability of
exceedance Design of earthquake effect is therefore termed as Earthquake Resistant Design
against the probable value of demand
Maximum Considered Earthquake (MCE) The earthquake corresponding to the Ultimate
Safety Requirement is often called as Maximum Considered Earthquake
Design Basis Earthquake (DBE) It is defined as the Maximum Earthquake that reasonably can
be expected to experience at the site during lifetime of structure
The philosophy of seismic design is to ensure that structures possess at least a minimum strength
to
(i) resist minor (lt DBE) which may occur frequently without damage
(ii) resist moderate earthquake (DBE) without significant structural damage through some
non-structural damage
(iii) resist major earthquake (MCE) without collapse
82 भको पी तवशलषण क तलए िरीक Methods for Seismic Analysis
The response of a structure to ground vibrations is a function of the nature of foundation soil
materials form size and mode of construction of structures and duration and characteristics of
ground motion Code specifies design forces for structures standing on rock or firm soils which
do not liquefy or slide due to loss of strength during ground motion
Analysis is carried out by
a- Dynamic analysis procedure [Clause 78 of IS 1893 (Part I) 2002]
b- Simplified method referred as Lateral Force Procedure [Clause 75 of IS 1893 (Part I)
2002] also recognized as Equivalent Lateral Force Procedure or Equivalent Static
Procedure in the literature
The main difference between the equivalent lateral force procedure and dynamic analysis
procedure lies in the magnitude and distribution of lateral forces over the height of the buildings
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49
In the dynamic analysis procedure the lateral forces are based on the properties of the natural
vibration modes of the building which are determined by the distribution of mass and stiffness
over height In the equivalent lateral force procedures the magnitude of forces is based on an
estimation of the fundamental period and on the distribution of forces as given by simple
formulae appropriate for regular buildings
83 िायनातमक तवशलषण Dynamic Analysis
Dynamic analysis shall be performed to obtain the design seismic force and its distribution to
different levels along the height of the building and to the various lateral load resisting elements
for the following buildings
a) Regular buildings ndash Those greater than 40 m in height in Zones IV and V and those greater
than 90 m in height in Zones II and III Modelling as per Para 7845 of IS 1893 (Part 1)
2002 can be used
b) Irregular buildings (as defined in Table ndash 61 and Table ndash 62 of Chapter - 6) ndash All framed
buildings higher than 12m in Zones IV and V and those greater than 40m in height in Zones
II and III
84 पारशय बल परतकरया Lateral Force Procedure
The random earthquake ground motions which cause the structure to vibrate can be resolved in
any three mutually perpendicular directions The predominant direction of ground vibration is
usually horizontal
The codes represent the earthquake-induced inertia forces in the form of design equivalent static
lateral force This force is called as the Design Seismic Base Shear VB VB remains the primary
quantity involved in force-based earthquake-resistant design of buildings
The Design Seismic Base Shear VB is given by
Where Ah = Design horizontal seismic coefficient for a structure
=
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50
Z = Zone Factor
It is for the Maximum Considered Earthquake (MCE) and service life of structure in a zone
Generally Design Basis Earthquake (DBE) is half of Maximum Considered Earthquake
(MCE) The factor 2 in the denominator of Z is used so as to reduce the MCE zone factor to
the factor for DBE
The value of Ah will not be taken less than Z2 whatsoever the value of IR
The value of Zone Factor is given in Table ndash 81
Table ndash 81 Zone Factor Z[IS 1893 (Part 1) 2002]
Seismic Zone II III IV V
Seismic Intensity Low Moderate Severe Very Severe
Zone Factor Z 010 016 024 036
I = Importance Factor
Value of importance factor depends upon the functional use of the structures characterized
by hazardous consequences of its failure post-earthquake functional needs historical value
or economic importance (as given in Table ndash 82)
Table ndash 82 Importance Factors I [IS 1893 (Part 1) 2002]
S
No
Structure Importance
Factor
(i) Important service and community buildings such as hospitals schools
monumental structures emergency buildings like telephone exchange
television stations radio stations railway stations fire station buildings
large community halls like cinemas assembly halls and subway stations
power stations
15
(ii) AU other buildings 10
Note
1 The design engineer may choose values of importance factor I greater than those
mentioned above
2 Buildings not covered in S No (i) and (ii) above may be designed for higher value of I
depending on economy strategy considerations like multi-storey buildings having
several residential units
3 This does not apply to temporary structures like excavations scaffolding etc of short
duration
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51
R = Response Reduction Factor
To make normal buildings economical design code allows some damage for reducing the
cost of construction This philosophy is introduced with the help of Response reduction
factor R
The ratio (IR) shall not be greater than 10
Depending on the perceived seismic damage performance of the structure by ductile or brittle
deformations the values of R1)
for buildings are given in Table ndash 83 below
Table ndash 83 Response Reduction Factor1)
R for Building Systems [IS 1893 (Part 1) 2002]
S No Lateral Load Resisting System R Building Frame Systems (i) Ordinary RC moment-resisting frame ( OMRF )
2) 30
(ii) Special RC moment-resisting frame ( SMRF )3)
50 (iii) Steel frame with
a) Concentric braces 40 b) Eccentric braces 50
(iv) Steel moment resisting frame designed as per SP 6 (6) 50 Building with Shear Walls
4)
(v) Load bearing masonry wall buildings5)
a) Unreinforced 15 b) Reinforced with horizontal RC bands 25 c) Reinforced with horizontal RC bands and vertical bars at cornersof
rooms and jambs of openings 30
(vi) Ordinary reinforced concrete shear walls6)
30 (vii) Ductile shear walls
7) 40
Buildings with Dual Systems8)
(viii) Ordinary shear wall with OMRF 30 (ix) Ordinary shear wall with SMRF 40 (x) Ductile shear wall with OMRF 45 (xi) Ductile shear wall with SMRF 50 1) The values of response reduction factor are to be used for buildings with lateral load resisting
elements and not just for the lateral load resisting elements built in isolation 2) OMRF (Ordinary Moment-Resisting Frame) are those designed and detailed as per IS 456 or
IS 800 but not meeting ductile detailing requirement as per IS 13920 or SP 6 (6) respectively 3) SMRF (Special Moment-Resisting Frame) defined in 4152
As per 4152 SMRF is a moment-resisting frame specially detailed to provide ductile behaviour and comply with the requirements given in IS 4326 or IS 13920 or SP 6 (6)
4) Buildings with shear walls also include buildings having shear walls and frames but where a) frames are not designed to carry lateral loads or b) frames are designed to carry lateral loads but do not fulfil the requirements of lsquodual
systemsrsquo 5) Reinforcement should be as per IS 4326 6) Prohibited in zones IV and V 7) Ductile shear walls are those designed and detailed as per IS 13920 8) Buildings with dual systems consist of shear walls ( or braced frames ) and moment resisting
frames such that a) the two systems are designed to resist the total design force in proportion to their lateral
stiffness considering the interaction of the dual system at all floor levels and b) the moment resisting frames are designed to independently resist at least 25 percent of the
design seismic base shear
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52
Sag = Average Response Acceleration Coefficient
Net shaking of a building is a combined effect of the energy carried by the earthquake at
different frequencies and the natural period (T) of the building Code reflects this by
introducing a structural flexibility factor (Sag) also termed as Design Acceleration
Coefficient
Design Acceleration Coefficient (Sag) corresponding to 5 damping for different soil
types normalized to Peak Ground Acceleration (PAG) corresponding to natural period (T)
of structure considering soil structure interaction given by Fig 81 and associated expression
given below
Table ndash 84 gives multiplying factors for obtaining spectral values for various other damping
Table ndash 84 Multiplying Factors for Obtaining Values for Other Damping [IS 1893 (Part 1) 2002]
Damping () 0 2 5 7 10 15 20 25 30
Factors 320 140 100 090 080 070 060 055 050
85 को पन की मौतलक पराकतिक अवतध Fundamental Natural Period of Vibration
The approximate fundamental natural period of vibration (Ta)in seconds of a moment-resisting
frame building without brick infill panels may be estimated by the empirical expression
Ta = 0075 h075
for RC frame building
= 0085 h075
for steel frame building
Where h = Height of building in m This excludes the basement storeys where
basement walls are connected with the ground floor deck or fitted between
the building columns But it includes the basement storeys when they are
not so connected
Fig 81 Response Spectra for Rock and Soil Sitesfor5 Damping [IS 1893 (Part 1) 2002]
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53
The approximate fundamental natural period of vibration (Ta) in seconds of all other buildings
including moment-resisting frame buildings with brick infill panels may be estimated by the
empirical expression
Where h = Height of building in m as defined above
d = Base dimension of the building at the plinth level in m along the
considered direction of the lateral force
86 तिजाइन पारशय बल Design Lateral Force
The total design lateral force or design seismic base shear (VB) along any principal direction shall
be determined by the following expression
Where Ah= Design horizontal acceleration spectrum value as per 642 using the
fundamental natural period Ta as per 76 in the considered direction of
vibration and
W= Seismic weight of the building
The design lateral force shall first be computed for the building as a whole This design lateral
force shall then be distributed to the various floor levels
The overall design seismic force thus obtained at each floor level shall then be distributed to
individual lateral load resisting elements depending on the floor diaphragm action
87 तिजाइन बल का तविरण Distribution of Design Force
871 Vertical Distribution of Base Shear to Different Floor Levels
The Design Seismic Base Shear (VB) as computed above shall be distributed along the height of
the building as per the following expression
Where
Qi= Design lateral force at floor i
Wi = Seismic weight of floor i
hi = Height of floor i measured from base and
n= Number of storeys in the building is the number of levels at which the masses are
located
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872 Distribution of Horizontal Design Lateral Force to Different Lateral Force Resisting
Elements
1 In case of buildings whose floors are capable of providing rigid horizontal diaphragm
action the total shear in any horizontal plane shall be distributed to the various vertical
elements of lateral force resisting system assuming the floors to be infinitely rigid in the
horizontal plane
2 In case of building whose floor diaphragms cannot be treated as infinitely rigid in their
own plane the lateral shear at each floor shall be distributed to the vertical elements
resisting the lateral forces considering the in-plane flexibility of the diaphragms
Notes
1 A floor diaphragm shall be considered to be flexible if it deforms such that the maximum
lateral displacement measured from the chord of the deformed shape at any point of the
diaphragm is more than 15 times the average displacement of the entire diaphragm
2 Reinforced concrete monolithic slab-beam floors or those consisting of prefabricated
precast elements with topping reinforced screed can be taken rigid diaphragms
88 तिजाइन उदािरण Design Example ndash To determine Base Shear and its distribution
along Height of Building
Exercise ndash 1 Determine the total base shear as per IS 1893(Part 1)2002 and distribute the base
shear along the height of building to be used as school building in Bhuj Gujrat and founded on
Medium Soil Basic parameters for design of building are as follows
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55
ELEVATION
Solution
Basic Data
Following basic data is considered for analysis
i) Grade of Concrete M-25
ii) Grade of Steel Fe ndash 415 Tor Steel
iii) Density of Concrete 25 KNm3
iv) Density of Brick Wall 20 KNm3
v) Live Load for Roof 15 KNm2
vi) Live Load for Floor 50 KNm2
vii) Slab Thickness 150 mm
viii) Beam Size
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56
(a) 500 m Span 250 mm X 600 mm
(b) 400 m Span 250 mm X 550 mm
(c) 200 m Span 250 mm X 400 mm
ix) Column Size
(a) For 500 m Span 300 mm X 600 mm
(b) For 200 m Span 300 mm X 500 mm
Load Calculations
1 Dead Load Building is of G+4 Storeys
Approximate Covered Area of Building on GF = 30 X 8 = 240 m2
Approximate Covered Area of 1st 2
nd 3
rd amp 4
th Floor = 240 m
2
Total Floor Area = 5 X 240 = 1200 m2
Roof Area = 1 X 240 = 240 m2
(I) Slab
Self Wt of Slab = 015 X 25 = 375 KNm2
Wt of Floor Finish = 125 KNm2
------------------------------
Total = 500 KNm2
Dead Load of Slab per Floor = 240 X 5 = 1200 KN
Dead Load of Slab on Roof = 240 X 5 = 1200 KN
(II) Beam
Wt per m of 250 X 600 mm beam = 025 X 060 X 25 = 375 KNm
Wt per m of 250 X 550 mm beam = 025 X 055 X 25 = 344 KNm
Wt per m of 250 X 400 mm beam = 025 X 040 X 25 = 250 KNm
Weight of Beam per Floor
= (2 X 30 X 375) + (4 X 6 + 30) X 344 + (2 X 6 X 250)
= 225 + 18576 + 30 = 44076 KN [Say 44100 KN]
(III) Column
Wt per m of 300 X 600 mm column = 030 X 060 X 25 = 450 KNm
Wt per m of 300 X 500 mm column = 030 X 050 X 25 = 375 KNm
Weight of Column per Floor
= (12 X 3 X 450) + (6 X 3 X 375)
= 162 + 6750 = 22950 KN [Say 23000 KN]
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57
Walls
250 mm thick wall (including plaster) are provided Assuming 20 opening in the
wall ndash
Wt of Wall per m = 025 X 080 X 20 X 250
Wall Thickness Reduction Density Clear Height
= 1000 KNm
Wt of Parapet Wall per m = 0125 X 20 X 100 = 250 KNm
Wall Thickness Density Clear Height
Wt of Wall per Floor = 1000 X [30 X 3 + 2 X 2] = 940 KN
Wt of Wall at Roof = 250 X [30 X 2 + 8 X 2] = 190 KN
Total Dead Load ndash
(i) For Floor = Slab + Beam + Column + Wall
= 1200 + 441 + 230 + 940 = 2811 KN
(ii) For Roof = 1200 + 441 + 190 = 1831 KN
Slab Beam Parapet
2 Live Load Live Load on Floor = 40 KNm2
As per Table ndash 8 in Cl 731 of IS 1893 (Part 1)2002 ldquoage of Imposed Load to be
considered in Seismic Weight calculationrdquo
(i) Up to amp including 300 KNm2 = 25
(ii) Above 300 KNm2 = 50
Live Load on Floors to be = 200 KNm2 [ie 50 of 40 KNm
2]
considered for Earthquake Force
As per Cl 732 of IS 1893 (Part 1)2002 for calculating the design seismic force of the
structure the imposed load on roof need not be considered
Therefore Live Load on Roof = 000 KN
Seismic Weight due to Live Load
(i) For Floor = 240 X 2 = 480 KN
(ii) For Roof = 000 KN
3 Seismic Weight of Building
As per Cl 74 of IS 1893 (Part 1)2002
(i) For Floor = DL of Floor + LL on Floor
= 2811 + 480 = 3291 KN
(ii) For Roof = 1831 + 000 = 1831 KN
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Total Seismic Weight of Building = 5 X 3291 + 1 X 1831
W = 18286 KN
4 Determination of Base Shear
As per Cl 75 of IS 1893 (Part 1)2002 VB = Ah W
Where
VB = Base Shear
Ah = Design Horizontal Acceleration Spectrum
=
W = Seismic Wt of Building
Total height of Building above Ground Level = 1500 m
As per Cl 76 of IS 1893 (Part 1)2002 Fundamental Natural Period of Vibration for RC
Frame Building is
Ta = 0075 h075
= 0075 (15)075
= 0572 Sec
Average Response Acceleration Coefficient = 25
for 5 damping and Type II soil
Bhuj Gujrat is in Seismic Zone V
As per Table ndash 2 of IS 1893 (Part 1)2002
Zone Factor Z = 036
As per Table ndash 6 of IS 1893 (Part 1)2002
Impedance Factor I = 150
As per Table ndash 7 of IS 1893 (Part 1)2002
Response Reduction Factor for Ordinary R = 300
RC Moment-resisting Frame (OMRF) Building
Ah =
= (0362) X (1530) X (25)
= 0225
Base Shear VB = Ah W
= 0225 X 18286
= 411435 KN [Say 411400 KN]
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5 Vertical Distribution of Base Shear to Different Floors Levels
As per Cl 771 of IS 1893 (Part 1)2002
Where
Qi= Design lateral force at floor i
Wi = Seismic weight of floor i
hi = Height of floor i measured from base and
n= Number of storeys in the building is the number of levels at which the masses are
located
VB = 4114 KN
Storey
No
Mass
No
Wi hi Wi hi2
f =
Qi = VB x f
(KN)
Vi
(KN)
Roof 1 1831 18 593244 0268 1103 1103
4th
Floor 2 3291 15 740475 0333 1370 2473
3rd
Floor 3 3291 12 473904 0213 876 3349
2nd
Floor 4 3291 9 266571 0120 494 3843
1st Floor 5 3291 6 118476 0053 218 4061
Ground 6 3291 3 29619 0013 53 4114
= 2222289
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60
अधयाय Chapter ndash 9
ढााचागि सोरचना का तनमायण Construction of Framed Structure
91 गरतवाकषयण लोतिोग और भको प लोतिोग म आर सी तबकडोग का वयविार Behaviour of RC
Building in Gravity Loading and Earthquake Loading
In recent times reinforced concrete buildings have become common in India particularly in
towns and cities A typical RC building consists of horizontal members (beams and slabs) and
vertical members (columns and walls) The system is supported by foundations that rest on
ground The RC frame participates in resisting the gravity and earthquake forces as illustrated in
Fig 91
Gravity Loading
1 Load due to self weight and contents on buildings cause RC frames to bend resulting in
stretching and shortening at various locations
2 Tension is generated at surfaces that stretch
and compression at those that shorten
3 Under gravity loads tension in the beams is
at the bottom surface of the beam in the
central location and is at the top surface at
the ends
Earthquake Loading
1 It causes tension on beam and column faces
at locations different from those under
gravity loading the relative levels of this
tension (in technical terms bending
moment) generated in members are shown
in Figure
2 The level of bending moment due to
earthquake loading depends on severity of
shaking and can exceed that due to gravity
loading
3 Under strong earthquake shaking the beam
ends can develop tension on either of the
top and bottom faces
4 Since concrete cannot carry this tension
steel bars are required on both faces of
beams to resist reversals of bending
moment
5 Similarly steel bars are required on all faces of columns too
Fig 91 Earthquake shaking reverses tension and
compression in members ndash reinforcement is
required on both faces of members
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61
92 परबतलि को करीट इमारिो ो पर कषतिज भको प का परभाव Effect of Horizontal Earthquake Force
on RC Buildings
Earthquake shaking generates inertia forces in the building which are proportional to the
building mass Since most of the building mass is present at floor levels earthquake-induced
inertia forces primarily develop at the floor
levels These forces travel downwards -
through slab and beams to columns and walls
and then to the foundations from where they
are dispersed to the ground (Fig 92)
As inertia forces accumulate downwards from
the top of the building the columns and walls
at lower storeys experience higher earthquake-
induced forces and are therefore designed to be
stronger than those in storeys above
93 कषमिा तिजाइन सोकलपना Capacity Design Concept
(i) Let us take two bars of same length amp Cross-sectional area
1st bar ndash Made up of Brittle Material
2nd
bar ndash Made up of Ductile Material
(ii) Pull both the bars until they break
(iii) Plot the graph of bar force F versus bar
elongation Graph will be as given in Fig
93
(iv) It is observed that ndash
a) Brittle bar breaks suddenly on reaching its
maximum strength at a relatively small
elongation
b) Ductile bar elongates by a large amount
before it breaks
Materials used in building construction are steel
masonry and concrete Steel is ductile material
while masonry and concrete are brittle material
Capacity design concept ensures that the brittle
element will remain elastic at all loads prior to the
failure of ductile element Thus brittle mode of
failure ie sudden failure has been prevented
Fig 92 Total horizontal earthquake force in a
building increase downwards along its height
Fig 93 Tension Test on Materials ndash ductile
versus brittle materials
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62
The concept of capacity design is used to ensure post-yield ductile behaviour of a structure
having both ductile and brittle elements In this method the ductile elements are designed and
detailed for the design forces Then an upper-bound strength of the ductile elements is obtained
It is then expected that if the seismic force keeps increasing a point will come when these ductile
elements will reach their upper-bound strength and become plastic Clearly it is necessary to
ensure that even at that level of seismic force the brittle elements remain safe
94 लचीलापन और ऊजाय का अपवयय Ductility and Energy Dissipation
From strength point of view overdesigned structures need not necessarily demonstrate good
ductility By ductility of Moment Resisting Frames (MRF) one refers to the capacity of the
structure and its elements to undergo large deformations without loosing either strength or
stiffness It is important for a building in a seismic zone to be resilient ie absorb the shock from
the ground and dissipate this energy uniformly throughout the structure
In MRFs the dissipation of the input seismic energy takes place in the form of flexural yielding
and resulting in the formation of plastic moment hinges Due to cyclic nature of the flexural
effects both positive and negative plastic moment hinges may be formed
95 मजबि सतोभ ndash कमजोर बीम फलोसफ़ी lsquoStrong Column ndash Weak Beamrsquo Philosophy
Because beams are usually capable of developing large ductility than columns which are
subjected to significant compressive loads many building frames are designed based on the
lsquostrong column ndash weak beamrsquo philosophy Figure shows that for a frame designed according to
the lsquostrong column ndash weak beamrsquo philosophy to form a failure mechanism many more plastic
hinges have to be formed than a
frame designed according to the
ldquoweak column ndash strong beamrsquo
philosophy The frames designed
by the former approach dissipate
greater energy before failure
When this strategy is adopted in
design damage is likely to occur
first in beams When beams are
detailed properly to have large
ductility the building as a whole
can deform by large amounts
despite progressive damage caused
due to consequent yielding of
beams
Note If columns are made weaker they suffer severe local damage at the top and bottom of a
particular storey This localized damage can lead to collapse of a building although columns at
storeys above remain almost undamaged (Fig 94)
Fig 94 Two distinct designs of buildings that result in different
earthquake performancesndashcolumns should be stronger than beams
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For a building to remain safe during earthquake shaking columns (which receive forces from
beams) should be stronger than beams and foundations (which receive forces from columns)
should be stronger than columns
96 कठोर िायाफराम तकरया Rigid Diaphragm Action
When beams bend in the vertical direction during earthquakes these thin slabs bend along with them And when beams move with columns in the horizontal direction the slab usually forces the beams to move together with it In most buildings the geometric distortion of the slab is negligible in the horizontal plane this behaviour is known as the rigid diaphragm action This aspect must be considered during design (Fig 95)
97 सॉफट सटोरी तबकडोग क साथ ndash ओपन गराउोि सटोरी तबकडोग जो तक भको प क समय कमजोर िोिी ि
Building with Soft storey ndash Open Ground Storey Building that is vulnerable in
Earthquake
The buildings that have been constructed in recent times with a special feature - the ground storey is left open for the purpose of parking ie columns in the ground storey do not have any partition walls (of either masonry or RC) between them are called open ground storey buildings or buildings on stilts
An open ground storey building (Fig 96) having only columns in the ground storey and both partition walls and columns in the upper storeys have two distinct characteristics namely
(a) It is relatively flexible in the ground storey ie the relative horizontal displacement it undergoes in the ground storey is much larger than what each of the storeys above it does This flexible ground storey is also called soft storey
(b) It is relatively weak in ground storey ie
the total horizontal earthquake force it can carry in the ground storey is significantly smaller than what each of the storeys above it can carry Thus the open ground storey may also be a weak storey
Fig 95 Floor bends with the beam but moves all
columns at that level together
Fig 96 Upper storeys of open ground storey building
move together as a single block ndash such buildings are
like inverted pendulums
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The collapse of more than a hundred RC frame buildings with open ground storeys at
Ahmedabad (~225km away from epicenter) during the 2001 Bhuj earthquake has emphasized
that such buildings are extremely vulnerable under earthquake shaking
After the collapses of RC buildings in 2001 Bhuj earthquake the Indian Seismic Code IS 1893
(Part 1) 2002 has included special design provisions related to soft storey buildings
Firstly it specifies when a building should be considered as a soft and a weak storey building
Secondly it specifies higher design forces for the soft storey as compared to the rest of the
structure
The Code suggests that the forces in the columns
beams and shear walls (if any) under the action of
seismic loads specified in the code may be
obtained by considering the bare frame building
(without any infills) However beams and
columns in the open ground storey are required to
be designed for 25 times the forces obtained
from this bare frame analysis (Fig 97)
For all new RC frame buildings the best option is
to avoid such sudden and large decrease in stiffness
andor strength in any storey it would be ideal to
build walls (either masonry or RC walls) in the
ground storey also Designers can avoid dangerous
effects of flexible and weak ground storeys by
ensuring that too many walls are not discontinued
in the ground storey ie the drop in stiffness and
strength in the ground storey level is not abrupt due
to the absence of infill walls (Fig 98)
The existing open ground storey buildings need to be strengthened suitably so as to prevent them
from collapsing during strong earthquake shaking The owners should seek the services of
qualified structural engineers who are able to suggest appropriate solutions to increase seismic
safety of these buildings
971 भरी हई दीवार In-Fill Walls
When columns receive horizontal forces at floor
levels they try to move in the horizontal direction
but masonry walls tend to resist this movement
Due to their heavy weight and thickness these
walls attract rather large horizontal forces
However since masonry is a brittle material these
walls develop cracks once their ability to carry
horizontal load is exceeded Thus infill walls act
like sacrificial fuses in buildings they develop
Fig 99 Infill walls move together with the
columns under earthquake shaking
Fig 97 Open ground storey building ndashassumptions
made in current design practice are not consistent
with the actual structure
Fig 98 Avoiding open ground storey problem ndash
continuity of walls in ground storey is preferred
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cracks under severe ground shaking but help share the load of the beams and columns until
cracking Earthquake performance of infill walls is enhanced by mortars of good strength
making proper masonry courses and proper packing of gaps between RC frame and masonry
infill walls (Fig 99)
98 भको प क दौरान लघ कॉलम वाली इमारिो ो का वयविार Behavior of Buildings with Short
Columns during Earthquakes
During past earthquakes reinforced concrete (RC) frame buildings that have columns of different heights within one storey suffered more damage in the shorter columns as compared to taller columns in the same storey
Two examples of buildings with short columns are shown in Fig 910 ndash (a) buildings on a sloping ground and (b) buildings with a mezzanine floor
Poor behaviour of short columns is due to the fact that in an earthquake a tall column and a short column of same cross-section move horizontally by same amount
However the short column is stiffer as compared
to the tall column and it attracts larger earthquake
force Stiffness of a column means resistance to
deformation ndash the larger is the stiffness larger is
the force required to deform it If a short column is
not adequately designed for such a large force it
can suffer significant damage during an
earthquake This behaviour is called Short Column
Effect (Fig 911)
In new buildings short column effect should be
avoided to the extent possible during architectural
design stage itself When it is not possible to avoid
short columns this effect must be addressed in
structural design The IS13920-1993for ductile
detailing of RC structures requires special
confining reinforcement to be provided over the
full height of columns that are likely to sustain
short column effect
Fig 910 Buildings with short columns ndash two
explicit examples of common occurrences
Fig 911 Short columns are stiffer and attract larger
forces during earthquakes ndash this must be accounted
for in design
Fig 912 Details of reinforcement in a building with
short column effect in some columns ndashadditional
special requirements are given in IS13920- 1993 for
the short columns
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The special confining reinforcement (ie closely spaced closed ties) must extend beyond the
short column into the columns vertically above and below by a certain distance as shown in
Fig 912
In existing buildings with short columns different retrofit solutions can be employed to avoid
damage in future earthquakes Where walls of partial height are present the simplest solution is
to close the openings by building a wall of full height ndash this will eliminate the short column
effect If that is not possible short columns need to be strengthened using one of the well
established retrofit techniques The retrofit solution should be designed by a qualified structural
engineer with requisite background
99 भको प परतिरोधी इमारिो ो की लचीलापन आवशयकिाएा Ductility requirements of
Earthquake Resistant Buildings
The primary members of structure such as beams and columns are subjected to stress reversals
from earthquake loads The reinforcement provided shall cater to the needs of reversal of
moments in beams and columns and at their junctions
Earthquake motion often induces forces large enough to cause inelastic deformations in the
structure If the structure is brittle sudden failure could occur But if the structure is made to
behave ductile it will be able to sustain the earthquake effects better with some deflection larger
than the yield deflection by absorption of energy Therefore besides the design for strength of
the frame ductility is also required as an essential element for safety from sudden collapse during
severe shocks
The ductility requirements will be deemed to be satisfied if the conditions given as in the
following are achieved
1 For all buildings which are more than 3 storeys in height the minimum grade of concrete
shall be M20 ( fck = 20 MPa )
2 Steel reinforcements of grade Fe 415 (IS 1786 1985) or less only shall be used
However high strength deformed steel bars produced by the thermo-mechanical treatment
process of grades Fe 500 and Fe 550 having elongation more than 145 percent and conforming
to other requirements of IS 1786 1985 may also be used for the reinforcement
910 बीम तजनह आर सी इमारिो ो म भको प बलो ो का तवरोध करन क तलए िाला जािा ि Beams that
are required to resist Earthquake Forces in RC Buildings
In RC buildings the vertical and horizontal members (ie the columns and beams) are built
integrally with each other Thus under the action of loads they act together as a frame
transferring forces from one to another
Beams in RC buildings have two sets of steel reinforcement (Fig 913) namely
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(a) long straight bars (called longitudinal bars)
placed along its length and
(b) closed loops of small diameter steel bars (called
stirrups)placed vertically at regular intervals
along its full length
Beams sustain two basic types of failures namely
(i) Flexural (or Bending) Failure
As the beam sags under increased loading it can
fail in two possible ways (Fig 914)
If relatively more steel is present on the tension
face concrete crushes in compression this is
a brittle failure and is therefore undesirable
If relatively less steel is present on the
tension face the steel yields first (it keeps
elongating but does not snap as steel has
ability to stretch large amounts before it
snaps and redistribution occurs in the beam
until eventually the concrete crushes in
compression this is a ductile failure and
hence is desirable Thus more steel on
tension face is not necessarily desirable The
ductile failure is characterized with many
vertical cracks starting from the stretched
beam face and going towards its mid-depth
(ii) Shear Failure
A beam may also fail due to shearing action A shear crack is inclined at 45deg to the horizontal it
develops at mid-depth near the support and grows towards the top and bottom faces Closed loop
stirrups are provided to avoid such shearing action Shear damage occurs when the area of these
stirrups is insufficient Shear failure is brittle and therefore shear failure must be avoided in the
design of RC beams
Longitudinal bars are provided to resist flexural
cracking on the side of the beam that stretches
Since both top and bottom faces stretch during
strong earthquake shaking longitudinal steel bars
are required on both faces at the ends and on the
bottom face at mid-length (Fig 915)
Fig 914 Two types of damage in a beam flexure
damage is preferred Longitudinal bars resist the
tension forces due to bending while vertical stirrups
resist shear forces
Fig 913 Steel reinforcement in beams ndash stirrups
prevent longitudinal bars from bending outwards
Fig 915 Location and amount of longitudinal steel
bars in beams ndash these resist tension due to flexure
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Designing a beam involves the selection of its material properties (ie grades of steel bars
and concrete) and shape and size these are usually selected as a part of an overall design
strategy of the whole building
The amount and distribution of steel to be provided in the beam must be determined by
performing design calculations as per IS 456-2000 and IS 13920-1993
911 फलकसचरल ममबसय क तलए सामानय आवशयकिाएा General Requirements for Flexural
Members
These members shall satisfy the following requirements
The member shall preferably have a width-to-depth ratio of more than 03
The width of the member shall not be less than 200 mm
The depth D of the member shall preferably be not more than 14 of the clear span
The factored axial stress on the member under earthquake loading shall not exceed 01fck
9111 अनदधयय सदढीकरण Longitudinal Reinforcement
a) The top as well as bottom reinforcement shall consist of at least two bars throughout the
member length
b) The tension steel ratio on any face at any section shall not be less than ρmin = 024 where fck
and fy are in MPa
The positive steel at a joint face must be at least equal to half the negative steel at that face
The steel provided at each of the top and bottom face of the member at any section along its
length shall be at least equal to one-fourth of the maximum negative moment steel provided
at the face of either joint It may be clarified that
redistribution of moments permitted in IS 456
1978 (clause 361) will be used only for vertical
load moments and not for lateral load moments
In an external joint both the top and the bottom
bars of the beam shall be provided with anchorage
length beyond the inner face of the column equal
to the development length in tension plus 10 times
the bar diameter minus the allowance for 90 degree
bend(s) (as shown in Fig 916) In an internal joint
both face bars of the beam shall be taken
continuously through the column
Fig 916 Anchorage of Beam Bars in an External Joint (IS 13920 1993)
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9112 अनदधयय सदढीकरण की सपलाइतसोग Splicing of longitudinal reinforcement
The longitudinal bars shall be spliced only if hoops are
provided over the entire splice length at a spacing not
exceeding 150 mm (as shown in Fig 917) The lap length
shall not be less than the bar development length in tension
Lap splices shall not be provided (a) within a joint (b)
within a distance of 2d from joint face and (c) within a
quarter length of the member where flexural yielding may
generally occur under the effect of earthquake forces Not
more than 50 percent of the bars shall be spliced at one
section
Use of welded splices and mechanical connections may also be made as per 25252 of
IS 456-1978 However not more than half the reinforcement shall be spliced at a section
where flexural yielding may take place
9113 वब सदढीकरण Web Reinforcement
Web reinforcement shall consist of vertical hoops A vertical hoop is a closed stirrup having a
135deg hook with a 10 diameter extension (but
not lt 75 mm) at each end that is embedded
in the confined core [as shown in (a) of
Fig 918] In compelling circumstances it
may also be made up of two pieces of
reinforcement a U-stirrup with a 135deg hook
and a 10 diameter extension (but not lt 75
mm) at each end embedded in the confined
core and a crosstie [as shown in (b) of Fig
918] A crosstie is a bar having a 135deg hook
with a 10 diameter extension (but not lt 75
mm) at each end The hooks shall engage
peripheral longitudinal bars
912 कॉलम तजनह आर सी इमारिो ो म भको प बलो ो का तवरोध करन क तलए िाला जािा ि Columns that are required to resist Earthquake Forces in RC Buildings
Columns the vertical members in RC buildings contain two types of steel reinforcement
namely
(a) long straight bars (called longitudinal bars) placed vertically along the length and
(b) closed loops of smaller diameter steel bars (called transverse ties) placed horizontally at
regular intervals along its full length
Fig 917 Lap Splice in Beam
(IS 13920 1993)
Fig 918 Beam Web Reinforcement (IS 13920 1993)
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Columns can sustain two types of damage namely axial-flexural (or combined compression-
bending) failure and shear failure Shear damage is brittle and must be avoided in columns by
providing transverse ties at close spacing
Closely spaced horizontal closed ties (Fig 919)
help in three ways namely
(i) they carry the horizontal shear forces
induced by earthquakes and thereby resist
diagonal shear cracks
(ii) they hold together the vertical bars and
prevent them from excessively bending
outwards(in technical terms this bending
phenomenon is called buckling) and
(iii) they contain the concrete in the column
within the closed loops The ends of the
ties must be bent as 135deg hooks Such hook
ends prevent opening of loops and
consequently bulging of concrete and
buckling of vertical bars
Construction drawings with clear details of closed ties are helpful in the effective implementation
at construction site In columns where the spacing between the corner bars exceeds 300mm the
Indian Standard prescribes additional links with 180deg hook ends for ties to be effective in holding
the concrete in its place and to prevent the buckling of vertical bars These links need to go
around both vertical bars and horizontal closed ties (Fig 920) special care is required to
implement this properly at site
Designing a column involves selection of
materials to be used (ie grades of concrete and
steel bars) choosing shape and size of the cross-
section and calculating amount and distribution
of steel reinforcement The first two aspects are
part of the overall design strategy of the whole
building The IS 13920 1993 requires columns
to be at least 300mm wide A column width of up
to 200 mm is allowed if unsupported length is less
than 4m and beam length is less than 5m
Columns that are required to resist earthquake
forces must be designed to prevent shear failure
by a skillful selection of reinforcement
Fig 919 Steel reinforcement in columns ndash closed ties
at close spacing improve the performance of column
under strong earthquake shaking
Fig 920 Extra links are required to keep the
concrete in place ndash 180deg links are necessary to
prevent the135deg tie from bulging outwards
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913 एकसीयल लोिि मबसय क तलए सामानय आवशयकिाएा General Requirements for Axial
Loaded Members
These requirements apply to frame members which have a factored axial stress in excess of
01 fck under the effect of earthquake forces
The minimum dimension of the member shall not be less than 200 mm However in frames
which have beams with centre to centre span exceeding 5 m or columns of unsupported
length exceeding 4 m the shortest dimension of the column shall not be less than 300 mm
The ratio of the shortest cross sectional dimension to the perpendicular dimension shall
preferably not be less than 04
9131 अनदधयय सदढीकरण Longitudinal Reinforcement
Lap splices shall be provided only in the central half
of the member length It should be proportioned as a
tension splice Hoops shall be provided over the
entire splice length at spacing not exceeding 150
mm centre to centre Not more than 50 percent of
the bars shall be spliced at one section
Any area of a column that extends more than 100
mm beyond the confined core due to architectural
requirements shall be detailed in the following
manner
a) In case the contribution of this area to strength
has been considered then it will have the minimum longitudinal and transverse
reinforcement as per IS 13920 1993
b) However if this area has been treated as non-structural the minimum reinforcement
requirements shall be governed by IS 456 1978 provisions minimum longitudinal and
transverse reinforcement as per IS 456 1978 (as shown in Fig 921)
9132 अनपरसथ सदढीकरण Transverse Reinforcement
Transverse reinforcement for circular columns shall consist of spiral or circular hoops In
rectangular columns rectangular hoops may be used A rectangular hoop is a closed stirrup
having a 135deg hook with a 10 diameter extension (but not lt 75 mm) at each end that is
embedded in the confined core [as shown in (A) of Fig 922]
Fig 921 Reinforcement requirement for Column with more than 100 mm projection beyond core(IS 13920 1993)
Fig 922 Transverse Reinforcement in Column (IS 13920 1993)
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The parallel legs of rectangular hoop shall be spaced not more than 300 mm centre to centre
If the length of any side of the hoop exceeds 300 mm a crosstie shall be provided [as shown
in (B) of Fig 922] Alternatively a pair of overlapping hoops may be provided within the
column [as shown in (C) of Fig 922] The hooks shall engage peripheral longitudinal bars
The spacing of hoops shall not exceed half the least lateral dimension of the column except
where special confining reinforcement is provided as per Para 915 below
914 बीम-कॉलम जोड़ जो आर सी भवनो ो म भको प बलो ो का तवरोध करि ि Beam-Column Joints
that resist Earthquakes Forces in RC Buildings
In RC buildings portions of columns that are
common to beams at their intersections are
called beam column joints (Fig 923) The
joints have limited force carrying capacity
When forces larger than these are applied
during earthquakes joints are severely
damaged Repairing damaged joints is
difficult and so damage must be avoided
Thus beam-column joints must be designed
to resist earthquake effects
Under earthquake shaking the beams adjoining a joint are subjected to moments in the same
(clockwise or counter-clockwise) direction
Under these moments the top bars in the
beam-column joint are pulled in one
direction and the bottom ones in the
opposite direction These forces are
balanced by bond stress developed between
concrete and steel in the joint region
(Fig 924)
If the column is not wide enough or if the
strength of concrete in the joint is low there
is insufficient grip of concrete on the steel
bars In such circumstances the bar slips
inside the joint region and beams loose
their capacity to carry load Further under
the action of the above pull-push forces at top and bottom ends joints undergo geometric
distortion one diagonal length of the joint elongates and the other compresses
If the column cross-sectional size is insufficient the concrete in the joint develops diagonal
cracks
Fig 923 Beam-Column Joints are critical parts of a
building ndash they need to be designed
Fig924 Pull-push forces on joints cause two
problems ndash these result in irreparable damage in joints
under strong seismic shaking
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9141 बीम-कॉलम जोड़ मजबि करन क तलए सामानय आवशयकिाएा General Requirements
for Reinforcing the Beam-Column Joint
Diagonal cracking and crushing of concrete in joint
region should be prevented to ensure good
earthquake performance of RC frame buildings
(Fig 925)
Using large column sizes is the most effective
way of achieving this
In addition closely spaced closed-loop steel ties
are required around column bars to hold
together concrete in joint region and to resist
shear forces
Intermediate column bars also are effective in
confining the joint concrete and resisting
horizontal shear forces Providing closed-loop
ties in the joint requires some extra effort
IS 13920ndash1993 recommends continuing the
transverse loops around the column bars
through the joint region
In practice this is achieved by preparing the cage of
the reinforcement (both longitudinal bars and
stirrups) of all beams at a floor level to be prepared
on top of the beam formwork of that level and
lowered into the cage (Fig 926)
However this may not always be possible
particularly when the beams are long and the entire
reinforcement cage becomes heavy
The gripping of beam bars in the joint region is
improved first by using columns of reasonably
large cross-sectional size
The Indian Standard IS 13920-1993 requires building columns in seismic zones III IV and V to
be at least 300mm wide in each direction of the cross-section when they support beams that are
longer than 5m or when these columns are taller than 4m between floors (or beams)
In exterior joints where beams terminate at columns longitudinal beam bars need to be anchored
into the column to ensure proper gripping of bar in joint The length of anchorage for a bar of
grade Fe415 (characteristic tensile strength of 415MPa) is about 50 times its diameter This
Fig 925 Closed loop steel ties in beam-column
joints ndash such ties with 135deg hooks resist the ill
effects of distortion of joints
Fig 926 Providing horizontal ties in the joints ndash
three-stage procedure is required
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length is measured from the face of the column to the end of the bar anchored in the column
(Fig 927)
In columns of small widths and when beam
bars are of large diameter (Fig 928(a)) a
portion of beam top bar is embedded in the
column that is cast up to the soffit of the
beam and a part of it overhangs It is difficult
to hold such an overhanging beam top bar in
position while casting the column up to the
soffit of the beam Moreover the vertical
distance beyond the 90ordm bend in beam bars is
not very effective in providing anchorage
On the other hand if column width is large
beam bars may not extend below soffit of the
beam (Fig 928 (b)) Thus it is preferable to
have columns with sufficient width
In interior joints the beam bars (both top and
bottom) need to go through the joint without
any cut in the joint region Also these bars
must be placed within the column bars and
with no bends
915 तवशष सीतमि सदढीकरण Special Confining Reinforcement
This requirement shall be met with unless a
larger amount of transverse reinforcement is
required from shear strength considerations
Special confining reinforcement shall be
provided over a length lsquolorsquo from each
joint face towards mid span and on
either side of any section where flexural
yielding may occur under the effect of
earthquake forces (as shown in Fig 929)
The length lsquolorsquo shall not be less than
(a) larger lateral dimension of the
member at the section where yielding
occurs
(b) 16 of clear span of the member and
(c) 450 mm
Fig 929 Column and Joint Detailing (IS 13920 1993)
Fig 927 Anchorage of beam bars in exterior
joints ndash diagrams show elevation of joint region
Fig 928 Anchorage of beam bars in interior
jointsndash diagrams (a) and (b) show cross-sectional
views in plan of joint region
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When a column terminates into a footing or mat special confining reinforcement shall extend
at least 300 mm into the footing or mat (as shown in Fig 930)
When the calculated point of contra-flexure
under the effect of gravity and earthquake
loads is not within the middle half of the
member clear height special confining
reinforcement shall be provided over the full
height of the column
Columns supporting reactions from discontinued stiff members such as walls shall be
provided with special confining reinforcement over their full height (as shown in Fig 931)
This reinforcement shall also be placed above the discontinuity for at least the development
length of the largest longitudinal bar in the column Where the column is supported on a wall
this reinforcement shall be provided
over the full height of the column it
shall also be provided below the
discontinuity for the same development
length
Special confining reinforcement shall
be provided over the full height of a
column which has significant variation
in stiffness along its height This
variation in stiffness may result due to
the presence of bracing a mezzanine
floor or a RCC wall on either side of
the column that extends only over a part
of the column height (as shown in Fig
931)
916 तवशषिः भको पीय कषतर म किरनी दीवारो ो वाली इमारिो ो का तनमायण Construction of Buildings
with Shear Walls preferably in Seismic Regions
Reinforced concrete (RC) buildings often have vertical
plate-like RC walls called Shear Walls in addition to
slabs beams and columns These walls generally start
at foundation level and are continuous throughout the
building height Their thickness can be as low as
150mm or as high as 400mm in high rise buildings
Shear walls are usually provided along both length and
width of buildings Shear walls are like vertically-
oriented wide beams that carry earthquake loads
downwards to the foundation (Fig 932)
Fig 932 Reinforced concrete shear walls in
buildings ndash an excellent structural system for
earthquake resistance
Fig 930 Provision of Special confining reinforcement in Footings (IS 13920 1993)
Fig 931 Special Confining Reinforcement Requirement for
Columns under Discontinued Walls (IS 13920 1993)
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Properly designed and detailed buildings with shear walls have shown very good performance in
past earthquakes Shear walls in high seismic regions require special detailing Shear walls are
efficient both in terms of construction cost and effectiveness in minimizing earthquake damage
in structural and non-structural elements (like glass windows and building contents)
Shear walls provide large strength and
stiffness to buildings in the direction of their
orientation which significantly reduces lateral
sway of the building and thereby reduces
damage to structure and its contents
Since shear walls carry large horizontal
earthquake forces the overturning effects on
them are large Thus design of their
foundations requires special attention
Shear walls should be provided along
preferably both length and width However if
they are provided along only one direction a
proper grid of beams and columns in the
vertical plane (called a moment-resistant
frame) must be provided along the other
direction to resist strong earthquake effects
Door or window openings can be provided in shear walls but their size must be small to
ensure least interruption to force flow through walls
Shear walls in buildings must be symmetrically located in plan to reduce ill-effects of twist in
buildings (Fig 933)
Shear walls are more effective when located along exterior perimeter of the building ndash such a
layout increases resistance of the building to twisting
9161 िनय तिजाइन और किरनी दीवारो ो की जयातमति Ductile Design and Geometry of Shear
Walls
Shear walls are oblong in cross-section ie one dimension of the cross-section is much larger
than the other While rectangular cross-section is common L- and U-shaped sections are also
used Overall geometric proportions of the wall types and amount of reinforcement and
connection with remaining elements in the building help in improving the ductility of walls The
Indian Standard Ductile Detailing Code for RC members (IS13920-1993) provides special
design guidelines for ductile detailing of shear walls
917 इमपरवड़ तिजाइन रणनीतियाो Improved design strategies
9171 िातनकारक भको प परभाव स भवनो ो का सोरकषण Protection of Buildings from Damaging
Earthquake Effects
Conventional seismic design attempts to make buildings that do not collapse under strong
earthquake shaking but may sustain damage to non-structural elements (like glass facades) and
to some structural members in the building There are two basic technologies ndashBase Isolation
Fig 933 Shear walls must be symmetric in plan
layout ndash twist in buildings can be avoided
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Devices and Seismic Dampers which are used to protect buildings from damaging earthquake
effects
9172 आधार अलगाव Base Isolation
The idea behind base isolation is to detach (isolate) the building from the ground in such a way
that earthquake motions are not transmitted up through the building or at least greatly reduced
As illustrated in Fig 934 when the ground shakes the rollers freely roll but the building
above does not move Thus no force is
transferred to the building due to shaking of
the ground simply the building does not
experience the earthquake
As illustrated in Fig 935 if the same
building is rested on flexible pads that offer
resistance against lateral movements then
some effect of the ground shaking will be
transferred to the building above
As illustrated in Fig 936 if the flexible
pads are properly chosen the forces induced
by ground shaking can be a few times
smaller than that experienced by the
building built directly on ground namely a
fixed base building
9173 भको पी सोज Seismic Dampers
Seismic dampers are special devices introduced in the building to absorb the energy provided by
the ground motion to the building These dampers act like the hydraulic shock absorbers in cars ndash
much of the sudden jerks are absorbed in the hydraulic fluids and only little is transmitted above
to the chassis of the car
When seismic energy is transmitted through them dampers absorb part of it and thus damp the
motion of the building Commonly used types of seismic dampers (Fig 937) include
Fig 934 Hypothetical Building
Fig 935 Base Isolated Building
Fig 936 Fixed-Base Building
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Viscous dampers ndash Energy is absorbed by
silicone-based fluid passing between piston-
cylinder arrangement
Friction dampers ndash Energy is absorbed by
surfaces with friction between them rubbing
against each other
Yielding dampers ndash Energy is absorbed by
metallic components that yield
In India friction dampers have been provided in an
18-storey RC frame structure in Gurgaon
918 तिजाइन उदािरण Design Example ndash Beam Design of RC Frame with Ductile
Detailing
Exercise ndash 2 Beam Design of RC Frame Building as per Provision of IS 13920 1993 and IS
1893 (Part 1) 2002 Beam marked ABC is considered for Design
Fig 937 Seismic Energy Dissipation Devices
each device is suitable for a certain building
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ELEVATION
Solution
1 General Data Grade of Concrete = M 25
Grade of steel = Fe 415 Tor Steel
2 Load Combinations
As per Cl 63 of IS 1893 (Part 1) 2002 following are load combinations for Earthquake
Loading
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S No Load Combination DL LL EQ Remark
1 15 DL + 15 LL 15 15 ndash As per Table ndash 8
of IS 1893 (Part
1) 2002 2 12 (DL + LL
+ EQx) 15 025 or 050 +12
3 12 (DL + LL ndash EQx) 15 025 or 050 ndash12
4 12 (DL + LL + EQy) 15 025 or 050 +12
5 12 (DL + LL ndash EQy) 15 025 or 050 ndash12
6 15 (DL + EQx) 15 +15
7 15 (DL ndash EQx) 15 ndash15
8 15 (DL + EQy) 15 +15
9 15 (DL ndash EQy) 15 ndash15
10 09 DL + 15 EQx 15 +15
11 09 DL ndash 15 EQx 15 ndash15
12 09 DL + 15 EQy 15 +15
13 09 DL ndash 15 EQy 15 ndash15
EQx implies EQ Loading in X ndash direction amp EQy implies EQ Loading in Y ndash direction
where X amp Y are orthogonal directions and Z is vertical direction These load combinations
are for EQ Loading In practice Wind Load should also be considered in lieu of EQ Load
and critical of the two should be used in the design
In this exercise emphasis is to show calculations for ductile design amp detailing of building
elements subjected to Earthquake in the plan considered Beams parallel to Y ndash direction are
not significantly affected by Earthquake force in X ndash direction (except in case of highly
unsymmetrical building) and vice versa Beams parallel to Y ndash direction are designed for
Earthquake loading in Y ndash direction only
Torsion effect is not considered in this example
3 Force Data
For Beam AB force resultants for various load cases (ie DL LL amp EQ Load) from
Computer Analysis (or manually by any method of analysis) to illustrate the procedure of
design are tabulated below
Table ndash A Force resultants in beam AB for various load cases
Load Case Left End Centre Right End
Shear
(KN)
Moment
(KN-m)
Shear
(KN)
Moment
(KN-m)
Shear
(KN)
Moment
(KN-m)
DL ndash 51 ndash 37 4 32 59 ndash 56
LL ndash 14 ndash 12 1 11 16 ndash 16
EQY 79 209 79 11 79 ndash 119
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Table ndash B Force resultants in beam AB for different load combinations
Load Combinations Left End Centre Right End
Shear
(KN)
Moment
(KN-m)
Shear
(KN)
Moment
(KN-m)
Shear
(KN)
Moment
(KN-m)
15 DL + 15 LL 98 ndash 74 7 64 111 ndash 108
12 (DL + LL + EQy) 31 205 101 52 172 ndash 303
12 (DL + LL ndash EQy) 162 ndash 300 92 31 22 159
15 (DL + EQy) 44 261 127 61 209 ndash 372
15 (DL ndash EQy) 97 ndash 371 115 34 33 205
09 DL + 15 EQy 75 283 124 42 174 ndash 339
09 DL ndash 15 EQy 167 ndash 349 117 15 68 238
4 Various checks for Flexure Member
(i) Check for Axial Stress
As per Cl 611 of IS 13920 1993 flexural axial stress on the member under EQ loading
shall not exceed 01 fck
Factored Axial Force = 000 KN
Factored Axial Stress = 000 MPa lt 010 fck OK
Hence the member is to be designed as Flexure Member
(ii) Check for Member size
As per Cl 613 of IS 13920 1993 width of the member shall not be less than 200 mm
Width of the Beam B = 250 mm gt 200 mm OK
Depth of Beam D = 550 mm
As per Cl 612 member shall have a width to depth ratio of more than 03
BD = 250550 = 04545 gt 03 OK
As per Cl 614 depth of member shall preferably be not more than 14 of the clear span
ie (DL) lt 14 or (LD) gt4
Span = 4 m LD = 4000550 = 727 gt 4 OK
Check for Limiting Longitudinal Reinforcement
Nominal cover to meet Durability requirements as per = 30 mm
Table ndash 16 of IS 4562000 (Cl 2642) for Moderate Exposure
Effective depth for Moderate Exposure conditions = 550 ndash 30 ndash 20 ndash (202)
with 20 mm of bars in two layers = 490 mm
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As per Cl 621 (b) of IS 13920 1993 tension steel ratio on any face at any section shall not
be less than = (024 radic fck) fy
= (024 radic25) 415 = 0289 asymp 029
Min Reinforcement = (029100) X 250 X 490 = 356 mm2
Max Reinforcement 25 = (25100) X 250 X 490 = 3063 mm2
(iii) Design for Flexure
Design for Hogging Moment at support A
At end A from Table ndash B Mu = 371 KN-m
Therefore Mu bd2 = 371x10
6 (250 x 490 x 490) = 618
Referring to Table ndash 51 of SP ndash 16 for drsquod = 55490 = 011
We get Ast at top = 2013 Asc = 0866
Therefore Ast at top = (2013100) x 250 x 490
= 2466 mm2
gt 356 mm2 (Min Reinforcement)
lt 3063 mm2 (Max Reinforcement)
Asc at bottom = 0866
As per Cl 623 of IS 13290 1993 positive steel at a joint face must be at least equal to half
the ndashve steel at that face Therefore Asc at bottom must be at least 50 of Ast hence
Revised Asc = 20132 = 10065
Asc at bottom = (10065100) x 250 x 490
= 1233 mm2 gt 426 mm
2 (Min Reinforcement)
lt 3063 mm2 (Max Reinforcement)
Design for Sagging Moment at support A
Mu = 283 KN-m
The beam will be designed as T-beam The limiting capacity of the T-beam assuming xu lt Df
and xu lt xumax may be calculated as follows
Mu = 087 fy Ast d [1- (Ast fy bf d fck)] -------- (Eq ndash 1)
Where Df = Depth of Flange
= 150 mm
xu = Depth of Neutral Axis
xumax = Limiting value of Neutral Axis
= 048 d
= 048 X 490
= 23520 mm
bw = 250 mm
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bf = Width of Flange
= (L06) + bw + 6 Df or cc of beam
= (07 X 40006) + 250 + 6 X 150
= 467 + 250 + 900 = 1617 mm or 4000 mm cc
[Lower of two is to be adopted]
Substituting the values in Eq ndash 1 and solving the quadratic equation
283 X 106 = 087 X 415 Ast X 490 [1ndash (Ast X 415) (1617 X 490 X 25)]
= 1769145 Ast [1 ndash 2095 X 10-5
Ast]
283 X 106 = 1769145 Ast ndash 3706 Ast
2]
3706 Ast2 ndash 1769145 Ast + 283 X 10
6 = 0
Ast = [1769145 plusmn radic(17691452 ndash 4 X 3706 X 283 X 10
6)] 2 X 3706
= [1769145 plusmn radic(3129874 X 1010
ndash 4195192 X 106)] 2 X 3706
= (1769145 plusmn 16463155) 7412
Ast at bottom = 165717 mm2 gt 35600 mm
2
lt 306300 mm2 OK
It is necessary to check the design assumptions before finalizing the reinforcement
xu = (087 fy Ast) (036 fck bf)
= (087 X 415 X 1657) (036 X 25 X 1617)
= 4110 mm lt 150 mm OK
lt df
lt xumax = 048 X 490 = 235 mm OK
Ast = [1657(250X490)] X 100 = 1353
As per Cl 624 ldquoSteel provided at each of the top amp bottom face of the member at any one
section along its length shall be at least equal to 14th
of the maximum (-ve) moment steel
provided at the face of either joint
For Centre Mu = 64 KN-m
64 X 106 = 087 X 415 Ast X 490 [1ndash (Ast X 415) (1617 X 490 X 25)]
= 1769145 Ast [1 ndash 2095 X 10-5
Ast]
64 X 106 = 1769145 Ast ndash 3706 Ast
2]
3706 Ast2 ndash 1769145 Ast + 64 X 10
6 = 0
Ast = [1769145 plusmn radic(17691452 ndash 4 X 3706 X 64 X 10
6)] 2 X 3706
= 365 mm2
For Right Support Mu = 238 KN-m
238 X 106 = 087 X 415 Ast X 490 [1ndash (Ast X 415) (1617 X 490 X 25)]
= 1769145 Ast [1 ndash 2095 X 10-5
Ast]
238 X 106 = 1769145 Ast ndash 3706 Ast
2]
3706 Ast2 ndash 1769145 Ast + 238 X 10
6 = 0
Ast = [1769145 plusmn radic(17691452 ndash 4 X 3706 X 238 X 10
6)] 2 X 3706
= 1386 mm2
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(iv) Reinforcement Requirement
Top reinforcement is larger of Ast at top for hogging moment or Asc at top for sagging
moment ie 2466 mm2 or 968 mm
2 Hence provide 2466 mm
2 at top
Bottom reinforcement is larger of Asc at bottom for hogging moment or Ast at bottom for
sagging moment ie 1233 mm2 or 1936 mm
2 Hence provide 1936 mm
2 at bottom
Details of Reinforcement
Top Reinforcement
Beam AB Left End Centre Right End
Hogging Moment ndash 371 - ndash 371
Mu bd2 618 - 618
Ast at top 2013 - 2013
Asc at bottom 0866 lt 2013 2 =
10065 Hence
revised Asc = 10065
- 0866
Revised to
10065 as per Cl
623 of IS
139201993
Bottom Reinforcement
Sagging Moment 283 64 238
Ast at bottom Ast req = 1657 mm2
= 1353
gt 20132 =
10065 OK
Provide Ast at bottom
= 1353
Ast req = 365 mm2
= 0298
gt 029
gt 20134 =
0504 OK
As per Cl 624 of IS
139201993
Provide Ast at bottom
= 0504
Ast req = 1386 mm2
= 117
gt 029
gt 20132 =
10065
Provide Ast at
bottom = 117
Asc at top Asc req = 1657 2
= 829 mm2
= 0677
gt 029
gt 2013 4 =
0504 OK
Asc req = 05042
= 0252
gt 029 Provide MinAsc = 029
Asc req = 1657 2
= 829 mm2
= 0677
gt 029
gt 2013 4
= 0504
OK
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Summary of Reinforcement required
Beam Left End Centre Right End
Top = 2013
= 2466 mm2
Bottom = 1353
= 1658 mm2
Top = 0504
= 618 mm2
Bottom = 0504
= 618 mm2
Top = 2013
= 2466 mm2
Bottom = 10065
= 1233 mm2
Reinforcement provided
2 ndash 20Φ cont + 4 ndash 25Φ extra
Ast = 2592 mm2 (2116)
2 ndash 20Φ cont + 2 ndash 20Φ extra
+ 2 ndash 16 Φ
Ast = 1658 mm2 (1353)
2 ndash 20Φ cont
Ast = 628 mm2 (0512)
2 ndash 20Φ cont
Ast = 628 mm2 (0512)
2 ndash 20Φ cont
+ 4 ndash 25Φ extra
Top = 2592 mm2
2 ndash 20Φ cont
+ 2 ndash 20Φ extra + 2 ndash 16Φ
Ast = 1658 mm2 (1353)
Details of Reinforcement
Ld = Development Length in tension
db = Dia of bar
For Fe 415 steel and M25 grade concrete as per Table ndash 65 of SP ndash 16
For 25Φ bars 1007 + 10Φ - 8Φ = 1007+50 = 1057 mm
For 20Φ bars 806 + 2Φ = 806+40 = 846 mm
(v) Design for Shear
Tensile steel provided at Left End = 2116
Permissible Design Stress of Concrete
(As per Table ndash 19 of IS 4562000) τc = 0835 MPa
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Design Shear Strength of Concrete = τc b d
= (0835 X 250 X 490) 1000
= 102 KN
Similarly Design Shear Strength of Concrete at centre for Ast = 0512
τc = 0493 MPa
Shear Strength of Concrete at centre = τc b d
= (0493 X 250 X 490) 1000
= 6040 KN
(vi) Shear force due to Plastic Hinge Formation at the ends of the beam
The additional shear due to formation of plastic hinges at both ends of the beams is evaluated
as per Cl 633 of IS 139201993 is given by
Vsway to right = plusmn 14 [MulimAs
+ MulimBh
] L
Vsway to left = plusmn 14 [MulimAh
+ MulimBs
] L
Where
MulimAs
= Sagging Ultimate Moment of Resistance of Beam Section at End A
MulimAh
= Hogging Ultimate Moment of Resistance of Beam Section at End A
MulimBh
= Sagging Ultimate Moment of Resistance of Beam Section at End B
MulimBs
= Hogging Ultimate Moment of Resistance of Beam Section at End B
At Ends beam is provided with steel ndash pt = 2116 pc = 1058
Referring Table 51 of SP ndash 16 for pt = 2116 pc = 1058
The lowest value of MuAh
bd2 is found
MuAh
bd2 = 645
Hogging Moment Capacity at End A
MuAh
= 645 X 250 X 4902
= 38716 X 108 N-mm
= 38716 KN-m
Similarly for MuAs
pt = 1058 pc = 2116
Contribution of Compressive steel is ignored while calculating the Sagging Moment
Capacity at T-beam
MuAs
= 087 fy Ast d [1- (Ast fy bf d fck)]
= 087 X 415 X 1658 X 490 [1ndash (1658 X 415 1617 X 490 X 25)]
= 28313 KN-m
Similarly for Right End of beam
MuBh
= 38716 KN-m amp MuBs
= 28313 KN-m
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Shear due to Plastic Hinge is calculated as
Vsway to right = plusmn 14 [MuAs
+ MuBh
] L
= plusmn 14 [28313 + 38716] 4
= 23460 KN
Vsway to left = plusmn 14 [MuAh
+ MuBs
] L
= plusmn 14 [38716 + 28313] 4
= 23460 KN
Design Shear
Dead Load of Slab = 50 KNm2 Live Load = 40 KNm
2
Load due to Slab in Beam AB = 2 X [12 X 4 X 2] X 5 = 40 KN (10 KNm)
Self Wt Of Beam = 025 X 055 X 25 X 4 = 1375 KN (344 KNm)
asymp 1400 KN
Live Load = 2 X [12 X 4 X 2] X 4 = 32 KN (8 KNm)
Shear Force due to DL = 12 X [40 + 14] = 27 KN
Shear Force due to LL = 12 X [32] = 16 KN
As per Cl 633 of IS 139201993 the Design shear at End A ie Vua and Design Shear at
End B ie Vub are computed as
(i) For Sway Right
Vua = VaD+L
ndash 14 [MulimAs
+ MulimBh
] LAB
Vub = VbD+L
+ 14 [MulimAs
+ MulimBh
] LAB
(ii) For Sway Left
Vua = VaD+L
+ 14 [MulimAh
+ MulimBs
] LAB
Vub = VbD+L
ndash 14 [MulimAh
+ MulimBs
] LAB
Where
VaD+L
amp VbD+L
= Shear at ends A amp B respectively due to vertical load with
Partial Safety Factor of 12 on Loads
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VaD+L
= VbD+L
= 12 (D+L) 2
--------------For equ (i)
---------------For equ (ii)
14 X [MuAs
+ MuBh
] L = 23460 KN
14 X [MuAh
+ MuBs
] L = 23460 KN
VaD = Vb
D = 12 X 27 = 324
= 516
VaL = Vb
L = 12 X 16 = 192
Vua = [12 (27+16)] ndash 23460 = 516 ndash 23460 = (-) 18300 KN
Vub = [12 (27+16)] + 23460 = 516 + 23460 = (+) 28620 KN
Vub = [12 (27+16)] + 23460 = 516 + 23460 = (+) 28620 KN
Vua = [12 (27+16)] ndash 23460 = 516 ndash 23460 = (-) 18300 KN
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As per Cl 633 of IS 139201993 the Design Shear Force to be resisted shall be of
maximum of
(i) Calculate factored SF as per analysis ( Refer Table ndash B)
(ii) Shear Force due to formation of Plastic Hinges at both ends of the beam plus
factored gravity load on the span
Hence Design shear Force Vu will be 28620 KN (corresponding to formation of Plastic
Hinge)
From Analysis as per Table ndash B SF at mid-span of the beam is 127 KN However Shear
due to formation of Plastic Hinge is 23460 KN Hence design shear at centre of span is
taken as 23460 KN
The required capacity of shear reinforcement at ends
Vus = Vu - Vc
= 28620 ndash 102
= 18420 KN
And at centre Vus = 23460 ndash 6040
= 17420 KN
At supports
Vus d = 28620 49 = 584 KNcm
Therefore requirement of stirrups is
12Φ ndash 2 legged strippus 135 cc [Vus d = 606]
However provide 12Φ ndash 2 legged strippus 120 cc as per provision of Cl 635 of IS
139201993 [Vus d = 6806]
At centre
Vus d = 23460 49 = 478 KNcm
Provide 12Φ ndash 2 legged strippus 170 cc [Vus d = 4804]
As per Cl 635 of IS 139201993 the spacing of stirrups in the mid-span should not
exceed d2 = 4902 = 245 mm
Minimum Shear Reinforcement as per Cl 26516 of IS 4562000 is
Sv = Asv X 08 fy 046
= (2 X 79 X 087 X 415) (250 X 04)
= 570 mm
As per CL 635 of IS 139201993 ldquoSpacing of Links over a length of 2d at either end of
beam shall not exceed
(i) d4 = 4904 = 12250 mm
(ii) 8 times dia of smallest longitudinal bar = 8 X 16 = 128 mm
However it need not be less than 100 mm
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The reinforcement detailing is shown as below
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अधयाय Chapter ndash 10
अलप सामरथय तचनाई सोरचनाओो क तनमायण Construction of Low Strength Masonry Structures
Two types of construction are included herein namely
a) Brick construction using weak mortar and
b) Random rubble and half-dressed stone masonry construction using different mortars such as
clay mud lime-sand and cement sand
101 भको प क दौरान ईोट तचनाई की दीवारो ो का वयविार Behaviour of Brick Masonry Walls
during Earthquakes
Of the three components of a masonry building (roof wall and foundation as illustrated in
Fig101) the walls are most vulnerable to damage caused by horizontal forces due to earthquake
Ground vibrations during earthquakes cause inertia forces at locations of mass in the building (Fig 102) These forces travel through the roof and walls to the foundation The main emphasis
is on ensuring that these forces reach the ground without causing major damage or collapse
A wall topples down easily if pushed
horizontally at the top in a direction
perpendicular to its plane (termed weak
Fig 101 Basic components of Masonry Building
Fig 103 For the direction of Earthquake shaking
shown wall B tends to fail
at its base
Fig 102 Effect of Inertia in a building when shaken
at its base
Fig 104 Direction of force on a wall critically determines
its earthquake performance
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direction) but offers much greater resistance if pushed along its length (termed strong direction) (Fig 103 amp 104)
The ground shakes simultaneously in the vertical and two horizontal directions during
earthquakes However the horizontal vibrations are the most damaging to normal masonry
buildings Horizontal inertia force developed at the
roof transfers to the walls acting either in the weak
or in the strong direction If all the walls are not tied
together like a box the walls loaded in their weak
direction tend to topple
To ensure good seismic performance all walls must
be joined properly to the adjacent walls In this way
walls loaded in their weak direction can take
advantage of the good lateral resistance offered by
walls loaded in their strong direction (Fig 105)
Further walls also need to be tied to the roof and
foundation to preserve their overall integrity
102 तचनाई वाली इमारिो ो म बॉकस एकशन कस सतनतिि कर How to ensure Box Action in
Masonry Buildings
A simple way of making these walls behave well during earthquake shaking is by making them
act together as a box along with the roof at the top and with the foundation at the bottom A
number of construction aspects are required to ensure this box action
Firstly connections between the walls should be good This can be achieved by (a) ensuring
good interlocking of the masonry courses at the junctions and (b) employing horizontal bands
at various levels particularly at the lintel level
Secondly the sizes of door and window
openings need to be kept small The smaller
the opening the larger is the resistance
offered by the wall
Thirdly the tendency of a wall to topple
when pushed in the weak direction can be
reduced by limiting its length-to-thickness
and height to-thickness ratios Design codes
specify limits for these ratios A wall that is
too tall or too long in comparison to its
thickness is particularly vulnerable to
shaking in its weak direction (Fig 106)
Fig 106 Slender walls are vulnerable
Fig 105 Wall B properly connected to Wall A
(Note roof is not shown) Walls A
(loaded in strong direction) support
Walls B (loaded in weak direction)
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Brick masonry buildings have large mass and hence attract large horizontal forces during
earthquake shaking They develop numerous cracks under both compressive and tensile forces
caused by earthquake shaking The focus of earthquake resistant masonry building construction
is to ensure that these effects are sustained without major damage or collapse Appropriate choice
of structural configuration can help achieve this
The structural configuration of masonry buildings
includes aspects like (a) overall shape and size of the
building and (b) distribution of mass and
(horizontal) lateral load resisting elements across the
building
Large tall long and un-symmetric buildings perform
poorly during earthquakes A strategy used in making
them earthquake resistant is developing good box
action between all the elements of the building ie
between roof walls and foundation (Fig 107) For
example a horizontal band introduced at the lintel
level ties the walls together and helps to make them
behave as a single unit
103 कषतिज बि की भतमका Role of Horizontal Bands
Horizontal bands are the most important
earthquake-resistant feature in masonry
buildings The bands are provided to hold a
masonry building as a single unit by tying all
the walls together and are similar to a closed
belt provided around cardboard boxes
(Fig 108 amp 109)
The lintel band undergoes bending and pulling actions during earthquake shaking
(Fig1010)
To resist these actions the construction of lintel band requires special attention
Fig 107 Essential requirements to ensure
box action in a masonry building
Fig 108 Building with flat roof
Fig 109 Two-storey Building with pitched roof
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Bands can be made of wood (including bamboo splits) or of reinforced concrete (RC) the
RC bands are the best (Fig 1011)
The straight lengths of the band must be properly connected at the wall corners
In wooden bands proper nailing of straight lengths with spacers is important
In RC bands adequate anchoring of steel links with steel bars is necessary
The lintel band is the most important of all and needs to be provided in almost all buildings
The gable band is employed only in buildings with pitched or sloped roofs
In buildings with flat reinforced concrete or reinforced brick roofs the roof band is not
required because the roof slab also plays the role of a band However in buildings with flat
timber or CGI sheet roof roof band needs to be provided In buildings with pitched or sloped
roof the roof band is very important
Plinth bands are primarily used when there is concern about uneven settlement of foundation
soil
Lintel band Lintel band is a band provided at lintel level on all load bearing internal external
longitudinal and cross walls
Roof band Roof band is a band provided immediately below the roof or floors Such a band
need not be provided underneath reinforced concrete or brick-work slabs resting on bearing
Fig 1010 Bending and pulling in lintel bands ndash Bands must be capable of resisting these actions
Fig 1011 Horizontal Bands in masonry buildings ndash RC bands are the best
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walls provided that the slabs are continuous over the intermediate wall up to the crumple
sections if any and cover the width of end walls fully or at least 34 of the wall thickness
Gable band Gable band is a band provided at the top of gable masonry below the purlins This
band shall be made continuous with the roof band at the eaves level
Plinth band Plinth band is a band provided at plinth level of walls on top of the foundation
wall This is to be provided where strip footings of masonry (other than reinforced concrete or
reinforced masonry) are used and the soil is either soft or uneven in its properties as frequently
happens in hill tracts This band will serve as damp proof course as well
104 अधोलोब सदढीकरण Vertical Reinforcement
Vertical steel at corners and junctions of walls which are up to 340 mm (1frac12 brick) thick shall be
provided as specified in Table 101 For walls thicker than 340 mm the area of the bars shall be
proportionately increased
No vertical steel need be provided in category A building The vertical reinforcement shall be
properly embedded in the plinth masonry of foundations and roof slab or roof band so as to
develop its tensile strength in bond It shall be passing through the lintel bands and floor slabs or
floor level bands in all storeys
Table ndash 101 Vertical Steel Reinforcement in Masonry Walls with Rectangular Masonry Units (IS 4326 1993)
No of Storeys Storey Diameter of HSD Single Bar in mm at Each Critical Section
Category B Category C Category D Category E One mdash Nil Nil 10 12
Two Top
Bottom
Nil
Nil
Nil
Nil
10
12
12
16
Three Top
Middle
Bottom
Nil
Nil
Nil
10
10
12
10
12
12
12
16
16
Four Top
Third
Second
Bottom
10
10
10
12
10
10
12
12
10
12
16
20
Four storeyed
building not
permitted
NOTES
1 The diameters given above are for HSD bars For mild-steel plain bars use equivalent diameters as given under
Table ndash 106 Note 2
2 The vertical bars will be covered with concrete M15 or mortar 1 3 grade in suitably created pockets around the
bars This will ensure their safety from corrosion and good bond with masonry
3 In case of floorsroofs with small precast components also refer 923 of IS 4326 1993 for floorroof band details
Bars in different storeys may be welded (IS 2751 1979 and IS 9417 1989 as relevant) or
suitably lapped
Vertical reinforcement at jambs of window and door openings shall be provided as per
Table ndash 101 It may start from foundation of floor and terminate in lintel band (Fig 1017)
Typical details of providing vertical steel in brickwork masonry with rectangular solid units
at corners and T-junctions are shown in Fig 1012
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105 दीवारो ो म सराखो ो का सोरकषण Protection of Openings in Walls
Horizontal bands including plinth band lintel band and roof band are provided in masonry
buildings to improve their earthquake performance Even if horizontal bands are provided
masonry buildings are weakened by the openings in their walls
Embedding vertical reinforcement bars in the edges of the wall piers and anchoring them in the
foundation at the bottom and in the roof band at the top forces the slender masonry piers to
undergo bending instead of rocking In wider wall piers the vertical bars enhance their capability
to resist horizontal earthquake forces and delay the X-cracking Adequate cross-sectional area of
these vertical bars prevents the bar from yielding in tension Further the vertical bars also help
protect the wall from sliding as well as from collapsing in the weak direction
However the most common damage observed after an earthquake is diagonal X-cracking of
wall piers and also inclined cracks at the corners of door and window openings
When a wall with an opening deforms during earthquake shaking the shape of the opening
distorts and becomes more like a rhombus - two opposite corners move away and the other two
come closer Under this type of deformation the corners that come closer develop cracks The
cracks are bigger when the opening sizes are larger Steel bars provided in the wall masonry all
Fig 1012 Typical Details of Providing Vertical Steel Bars in Brick Masonry (IS 4326 1993)
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around the openings restrict these cracks at the corners In summary lintel and sill bands above
and below openings and vertical reinforcement adjacent to vertical edges provide protection
against this type of damage (Fig 1013)
106 भको प परतिरोधी ईोट तचनाई भवन क तनमायण िि सामानय तसदाोि General Principles for
Construction of Earthquake Resistant Brick Masonry Building
Low Strength Masonry constructions should not be permitted for important buildings
It will be useful to provide damp-proof course at plinth level to stop the rise of pore water
into the superstructure
Precautions should be taken to keep the rain water away from soaking into the wall so that
the mortar is not softened due to wetness An effective way is to take out roof projections
beyond the walls by about 500 mm
Use of a water-proof plaster on outside face of walls will enhance the life of the building and
maintain its strength at the time of earthquake as well
Ignoring tensile strength free standing walls should be checked against overturning under the
action of design seismic coefficient ah allowing for a factor of safety of 15
1061 भवनो ो की शरतणयाा Categories of Buildings
For the purpose of specifying the earthquake resistant features in masonry and wooden buildings
the buildings have been categorized in five categories A to E based on the seismic zone and the
importance of building I
Where
I = importance factor applicable to the
building [Ref Clause 642 and
Table - 6 of IS 1893 (Part 1) 2002]
The building categories are given in
Table ndash 102
Fig 1013 Cracks at corners of openings in a masonry building ndash reinforcement around them helps
Table -102 Building Categories for Earthquake Resisting Features (IS 4326 1993)
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1062 कमजोर गार म ईोट तचनाई कायय Brickwork in Weak Mortars
The fired bricks should have a compressive strength not less than 35 MPa Strength of bricks
and wall thickness should he selected for the total building height
The mortar should be lime-sand (13) or clay mud of good quality Where horizontal steel is
used between courses cement-sand mortar (13) should be used with thickness so as to cover
the steel with 6 mm mortar above and below it Where vertical steel is used the surrounding
brickwork of 1 X 1 or lfrac12 X 1frac12 brick size depending on wall thickness should preferably be
built using 16 cement-sand mortar
The minimum wall thickness shall be one brick in one storey construction and one brick in
top storey and 1frac12brick in bottom storeys of up to three storey constructions It should also
not be less than l16 of the length of wall between two consecutive perpendicular walls
The height of the building shall be restricted to the following where each storey height shall
not exceed 30 m
For Categories A B and C - three storeys with flat roof and two storeys plus attic pitched
roof
For Category D - two storeys with flat roof and one storey plus attic for pitched roof
1063 आयिाकार तचनाई इकाइयो ो वाला तचनाई तनमायण Masonry Construction with
Rectangular Masonry Units
General requirements for construction of masonry walls using rectangular masonry units are
10631 तचनाई इकाइयाो Masonry Units
Well burnt bricks conforming to IS 1077 1992 or solid concrete blocks conforming to IS
2185 (Part 1) 1979 and having a crushing strength not less than 35 MPa shall be used The
strength of masonry unit required
shall depend on the number of storeys
and thickness of walls
Squared stone masonry stone block
masonry or hollow concrete block
masonry as specified in IS 1597 (Part
2) 1992 of adequate strength may
also be used
10632 गारा Mortar
Mortars such as those given in Table
ndash 103 or of equivalent specification
shall preferably be used for masonry
Table ndash 103 Recommended Mortar Mixes (IS 4326 1993)
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construction for various categories of buildings
Where steel reinforcing bars are provided in masonry the bars shall be embedded with
adequate cover in cement sand mortar not leaner than 13 (minimum clear cover 10 mm) or in
cement concrete of grade M15 (minimum clear cover 15 mm or bar diameter whichever
more) so as to achieve good bond and corrosion resistance
1064 दीवार Walls
Masonry bearing walls built in mortar as specified in 10632 above unless rationally
designed as reinforced masonry shall not be built of greater height than 15 m subject to a
maximum of four storeys when measured from the mean ground level to the roof slab or
ridge level
The bearing walls in both directions shall be straight and symmetrical in plan as far as
possible
The wall panels formed between cross walls and floors or roof shall be checked for their
strength in bending as a plate or as a vertical strip subjected to the earthquake force acting on
its own mass
Note mdash For panel walls of 200 mm or larger thickness having a storey height not more than
35 metres and laterally supported at the top this check need not be exercised
1065 तचनाई बॉणड Masonry Bond
For achieving full strength of
masonry the usual bonds
specified for masonry should be
followed so that the vertical joints
are broken properly from course
to course To obtain full bond
between perpendicular walls it is
necessary to make a slopping
(stepped) joint by making the
corners first to a height of 600
mm and then building the wall in
between them Otherwise the
toothed joint (as shown in Fig
1014) should be made in both the
walls alternatively in lifts of
about 450 mm
Panel or filler walls in framed buildings shall be properly bonded to surrounding framing
members by means of suitable mortar (as given in 10632 above) or connected through
dowels
Fig 1014 Alternating Toothed Joints in Walls at Corner and T-Junction (IS 4326 1993)
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107 ओपतनोग का परभाव Influence of Openings
Openings are functional necessities in buildings
During earthquake shaking inertia forces act in
the strong direction of some walls and in the weak
direction of others Walls shaken in the weak
direction seek support from the other walls ie
walls B1 and B2 seek support from walls A1 and
A2 for shaking in the direction To be more
specific wall B1 pulls walls A1 and A2 while
wall B2 pushes against them
Thus walls transfer loads to each other at their
junctions (and through the lintel bands and roof)
Hence the masonry courses from the walls
meeting at corners must have good interlocking
(Fig 1015) For this reason openings near the
wall corners are detrimental to good seismic
performance Openings too close to wall corners
hamper the flow of forces from one wall to
another Further large openings weaken walls
from carrying the inertia forces in their own
plane Thus it is best to keep all openings as small as possible and as far away from the corners
as possible
108 धारक दीवारो ो म ओपतनोग परदाि करि की सामानय आवशयकताए General Requirements of
Providing Openings in Bearing Walls
Door and window openings in walls reduce their lateral load resistance and hence should
preferably be small and more centrally located The guidelines on the size and position of
opening are given in Table ndash 104 and in Fig 1016
Fig 1015 Regions of force transfer from weak
walls to strong walls in a masonry building ndash Wall
B1 pulls walls A1 and A2 while wall B2pushes walls
A1 and A2
Fig 1016 Dimensions of Openings and Piers for
Recommendations in Table 3 (IS 4326 1993)
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Table ndash 104 Size and Position of Openings in Bearing Walls
S
No
Position of opening Details of Opening for Building Category
A and B C D and E
1 Distance b5 from the inside corner of outside wall Min Zero mm 230 mm 450 mm
2 For total length of openings the ratio (b1+b2+b3)l1 or
(b6+b7)l2 shall not exceed
a) one-storeyed building
b) two-storeyed building
c) 3 or 4-storeyed building
060
050
042
055
046
037
050
042
033
3 Pier width between consecutive openings b4 Min 340 mm 450 mm 560 mm
4 Vertical distance between two openings one above the
other h3 Min
600 mm 600 mm 600 mm
5 Width of opening of ventilator b8 Max 900 mm 900 mm 900 mm
Openings in any storey shall preferably have their top at the same level so that a continuous
band could be provided over them including the lintels throughout the building
Where openings do not comply with the guidelines as given in Table ndash 104 they should be
strengthened by providing reinforced concrete or reinforcing the brickwork as shown in Fig
1017 with high strength deformed (HSD) bars of 8 mm dia but the quantity of steel shall be
increased at the jambs
If a window or ventilator is to be
projected out the projection shall be in
reinforced masonry or concrete and well
anchored
If an opening is tall from bottom to
almost top of a storey thus dividing the
wall into two portions these portions
shall be reinforced with horizontal
reinforcement of 6 mm diameter bars at
not more than 450 mm intervals one on
inner and one on outer face properly tied
to vertical steel at jambs corners or
junction of walls where used
The use of arches to span over the
openings is a source of weakness and
shall be avoided Otherwise steel ties
should be provided
109 भको पी सदढ़ीकरण वयवसथा Seismic Strengthening Arrangements
All masonry buildings shall be strengthened as specified for various categories of buildings as
listed in Table ndash 105
Fig 1017 Strengthening Masonry around Opening (IS
4326 1993)
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Table ndash 105 Strengthening Arrangements Recommended for Masonry Buildings
(Rectangular Masonry Units)(IS 4326 1993)
Building Category Number of Storeyes Strengthening to be Provided in all Storeys
A
i) 1 to 3
ii) 4
a
a b c
B
i) 1 to 3
ii) 4
a b c f g
a b c d f g
C
i) 1 and 2
ii) 3 and 4
a b c f g
a to g
D
i) 1 and 2
ii) 3 and 4
a to g
a to h
E 1 to 3 a to h
Where
a mdash Masonry mortar
b mdash Lintel band
c mdash Roof band and gable band where necessary
d mdash Vertical steel at corners and junctions of walls
e mdash Vertical steel at jambs of openings
f mdash Bracing in plan at tie level of roofs
g mdash Plinth band where necessary and
h mdash Dowel bars
4th storey not allowed in category E
NOTE mdash In case of four storey buildings of category B the requirements of vertical steel may be checked
through a seismic analysis using a design seismic coefficient equal to four times the one given in (a) 3423
of IS 1893 1984 (This is because the brittle behaviour of masonry in the absence of vertical steel results in
much higher effective seismic force than that envisaged in the seismic coefficient provided in the code) If
this analysis shows that vertical steel is not required the designer may take the decision accordingly
The overall strengthening arrangements to be adopted for category D and E buildings which
consist of horizontal bands of reinforcement at critical levels vertical reinforcing bars at corners
junctions of walls and jambs of opening are shown in Fig 1018 amp 1019
Fig 1018 Overall Arrangement of Reinforcing Fig 1019 Overall Arrangement of Reinforcing Masonry
Masonry Buildings (IS 4326 1993) Building having Pitched Roof (IS 4326 1993)
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103
1091 पटट का अनभाग एवो सदढीकरण Section and Reinforcement of Band
The band shall be made of reinforced concrete of grade not leaner than M15 or reinforced
brickwork in cement mortar not leaner than 13 The bands shall be of the full width of the wall
not less than 75 mm in depth and reinforced with steel as indicated in Table ndash 106
Table ndash 106 Recommended Longitudinal Steel in Reinforced Concrete Bands (IS 4326 1993)
Span Building Category
B
Building Category
C
Building Category
D
Building Category
E No of Bars Dia No of Bars Dia No of Bars Dia No of Bars Dia
(1) (2) (3) (4) (5) (6) (7) (8) (9)
m mm mm mm mm
5 or less 2 8 2 8 2 8 2 10
6 2 8 2 8 2 10 2 12
7 2 8 2 10 2 12 4 10
8 2 10 2 12 4 10 4 12
Notes -
1 Span of wall will be the distance between centre lines of its cross walls or buttresses For spans greater than 8 m
it will be desirable to insert pillasters or buttresses to reduce the span or special calculations shall be made to
determine the strength of wall and section of band
2 The number and diameter of bars given above pertain to high strength deformed bars If plain mild-steel bars are
used keeping the same number the following diameters may be used
High Strength Def Bar dia 8 10 12 16 20
Mild Steel Plain bar dia 10 12 16 20 25
3 Width of RC band is assumed same as the thickness of the wall Wall thickness shall be 200 mm minimum A
clear cover of 20 mm from face of wall will be maintained
4 The vertical thickness of RC band be kept 75 mm minimum where two longitudinal bars are specified one on
each face and 150 mm where four bars are specified
5 Concrete mix shall be of grade M15 of IS 456 1978 or 1 2 4 by volume
6 The longitudinal steel bars shall be held in position by steel links or stirrups 6 mm dia spaced at 150 mm apart
NOTE mdash In coastal areas the concrete grade shall be M20 concrete and the filling mortar of 13
(cement-sand with water proofing admixture)
As illustrated in Fig 1020 ndash
In case of reinforced brickwork the
thickness of joints containing steel bars shall
be increased so as to have a minimum
mortar cover of 10 mm around the bar In
bands of reinforced brickwork the area of
steel provided should be equal to that
specified above for reinforced concrete
bands
In category D and E buildings to further
iterate the box action of walls steel dowel
bars may be used at corners and T-junctions
of walls at the sill level of windows to
length of 900 mm from the inside corner in
each wall Such dowel may be in the form of
Fig 1020 Reinforcement and Bending Detail in RC Band ((IS 4326 1993)
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U stirrups 8 mm dia Where used such bars must be laid in 13 cement-sand-mortar with a
minimum cover of 10 mm on all sides to minimize corrosion
1010 भको प क दौरान सटोन तचनाई की दीवारो ो का वयविार Behaviour of Stone Masonry
Walls during Earthquakes
Stone has been used in building construction in India since ancient times since it is durable and
locally available The buildings made of thick stone masonry walls (thickness ranges from 600 to
1200 mm) are one of the most deficient building systems from earthquake-resistance point of
view
The main deficiencies include excessive wall thickness absence of any connection between the
two wythes of the wall and use of round stones (instead of shaped ones) (Fig 1021 amp 1022)
Note A wythe is a continuous vertical section of masonry one unit in thickness A wythe may be
independent of or interlocked with the adjoining wythe (s) A single wythe of brick that is not
structural in nature is referred to as a veneer (httpsenwikipediaorgwikiWythe)
The main patterns of earthquake damage include
(a) bulging separation of walls in the horizontal direction into two distinct wythes
(b) separation of walls at corners and T-junctions
(c) separation of poorly constructed roof from walls and eventual collapse of roof and
(d) disintegration of walls and eventual collapse of the whole dwelling
In the 1993 Killari (Maharashtra) earthquake alone over 8000 people died most of them buried
under the rubble of traditional stone masonry dwellings Likewise a majority of the over 13800
deaths during 2001 Bhuj (Gujarat) earthquake is attributed to the collapse of this type of
construction
1011 भको प परतिरोधी सटोन तचनाई भवन क तनमायण िि सामानय तसदाोि General principle for
construction of Earthquake Resistant stone masonry building
10111 भको प परतिरोधी लकषण Earthquake Resistant Features
1 Low strength stone masonry buildings are weak against earthquakes and should be avoided
in high seismic zones Inclusion of special earthquake-resistant features may enhance the
earthquake resistance of these buildings and reduce the loss of life These features include
Fig 1021 Separation of a thick wall into two layers Fig 1022 Separation of unconnected adjacent walls at junction
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(a) Ensure proper wall construction
(b) Ensure proper bond in masonry courses
(c) Provide horizontal reinforcing elements
(d) Control on overall dimensions and heights
2 The mortar should be cement-sand (1 6) lime-sand (1 3) or clay mud of good quality
3 The wall thickness should not be larger than 450
mm Preferably it should be about 350 mm and
the stones on the inner and outer wythes should be
interlocked with each other
NOTE - If the two wythes are not interlocked they
tend to delaminate during ground shaking bulge
apart (as shown in Fig 1023) and buckle
separately under vertical load leading to
complete collapse of the wall and the building
4 The masonry should preferably be brought to courses at not more than 600 mm lift
5 lsquoThroughrsquo stones at full length
equal to wall thickness should be
used in every 600 mm lift at not
more than 12 m apart
horizontally If full length stones
are not available stones in pairs
each of about 34 of the wall
thickness may be used in place of
one full length stone so as to
provide an overlap between them
(as shown in Fig 1024)
6 In place of lsquothroughrsquo stones lsquobonding elementsrsquo of steel bars 8 to 10 mm dia bent to S-shape
or as hooked links may be used with a cover of 25 mm from each face of the wall (as shown
in Fig 1024) Alternatively wood-bars of 38 mm X 38 mm cross section or concrete bars of
50 mm X50 mm section with an 8 mm dia rod placed centrally may be used in place of
throughrsquo stones The wood should be well treated with preservative so that it is durable
against weathering and insect action
7 Use of lsquobondingrsquo elements of adequate length should also be made at corners and junctions of
walls to break the vertical joints and provide bonding between perpendicular walls
8 Height of the stone masonry walls (random rubble or half-dressed) should be restricted as
follows with storey height to be kept 30 m maximum and span of walls between cross walls
to be limited to 50 m
Fig 1023 Wall delaminated with buckled
withes (IS 13828 1993)
Fig 1024 Through Stone and Bond Elements (IS 13828 1993)
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a) For categories A and B ndash Two storeys with flat roof or one storey plus attic if walls are
built in lime-sand or mud mortar and -one storey higher if walls are built in cement-sand
1 6 mortar
b) For categories C and D - Two storeys with flat roof or two storeys plus attic for pitched
roof if walls are built in 1 6 cement mortar and one storey with flat roof or one storey
plus attic if walls are built in lime-sand or mud mortar respectively
9 If walls longer than 5 m are needed buttresses may be used at intermediate points not farther
apart than 40 m The size of the buttress be kept of uniform thickness Top width should be
equal to the thickness of main wall t and the base width equal to one sixth of wall height
10 The stone masonry dwellings must have horizontal bands (plinth lintel roof and gable
bands) These bands can be constructed out of wood or reinforced concrete and chosen based
on economy It is important to provide at least one band (either lintel band or roof band) in
stone masonry construction
Note Although this type of stone masonry construction practice is deficient with regards to earthquake
resistance its extensive use is likely to continue due to tradition and low cost But to protect human lives
and property in future earthquakes it is necessary to follow proper stone masonry construction in seismic
zones III and higher Also the use of seismic bands is highly recommended
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अधयाय Chapter- 11
भकपीय रलयमकन और रटरोफिट ग
SEISMIC EVALUATION AND RETROFITTING
There are considerable number of buildings that do not meet the requirements of current design
standards because of inadequate design or construction errors and need structural upgrading
specially to meet the seismic requirements
Retrofitting is the best solution to strengthen such buildings without replacing them
111 भकपीय रलयमकन SEISMIC EVALUATION
Seismic evaluation is to assess the seismic response of buildings which may be seismically
deficient or earthquake damaged for their future use The evaluation is also helpful in choosing
appropriate retrofitting techniques
The methods available for seismic evaluation of existing buildings can be broadly divided into
two categories
1 Qualitative methods 2 Analytical methods
1111 गणमतरक िरीक QUALITATIVE METHODS
The qualitative methods are based on the available background information of the structures
past performance of similar structures under severe earthquakes visual inspection report some
non-destructive test results etc
Method for Seismic evaluation
Qualitative methods Analytic methods
CapacityDemand
method
Push over
analysis
Inelastic time
history method
Condition
assessment
Visual
inspection
Non-destructive
testing
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The evaluation of any building is a difficult task which requires a wide knowledge about the
structures cause and nature of damage in structures and its components material strength etc
The proposed methodology is divided into three components
1 Condition assessment
It is based on
data collection or information gathering of structures from architectural and structural
drawings
performance characteristics of similar type of buildings in past earthquakes
rapid evaluation of strength drift materials structural components and structural details
2 Visual inspectionField evaluation It is based on observed distress and damage in
structures Visual inspection is more useful for damaged structures however it may also be
conducted for undamaged structures
3 Non-destructive evaluation It is generally carried out for quick estimation of materials
strength determination of the extent of determination and to establish causes remain out of
reach from visual inspection and determination of reinforcement and its location NDT may
also be used for preparation of drawing in case of non-availability
11111 Condition Assessment for Evaluation
The aim of condition assessment of the structure is the collection of information about the
structure and its past performance characteristics to similar type of structure during past
earthquakes and the qualitative evaluation of structure for decision-making purpose More
information can be included if necessary as per requirement
(i) Data collection information gathering
Collection of the data is an important portion for the seismic evaluation of any existing building
The information required for the evaluated building can be divided as follows
Building Data
Architectural structural and construction drawings
Vulnerability parameters number of stories year of construction and total floor area
Specification soil reports and design calculations
Seismicity of the site
Construction Data
Identifications of gravity load resisting system
Identifications of lateral load resisting system
Maintenance addition alteration or modifications in structures
Field surveys of the structurersquos existing condition
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Structural Data
Materials
Structural concept vertical and horizontal irregularities torsional eccentricity pounding
short column and others
Detailing concept ductile detailing special confinement reinforcement
Foundations
Non-structural elements
(ii) Past Performance data
Past performance of similar type of structure during the earthquake provides considerable amount
of information for the building which is under evaluation process Following are the areas of
concerns which are responsible for poor performance of buildings during earthquake
Material concerns
Low grade on concrete
Deterioration in concrete and reinforcement
High cement-sand ratio
Corrosion in reinforcement
Use of recycled steel as reinforcement
Spalling of concrete by the corrosion of embedded reinforcing bars
Corrosion related to insufficient concrete cover
Poor concrete placement and porous concrete
Structural concerns
The relatively low stiffness of the frames excessive inter-storey drifts damage to non-
structural items
Pounding column distress possibly local collapse
Unsymmetrical buildings (U T L V) in plan torsional effects and concentration of damage
at the junctures (ie re-entrant corners)
Unsymmetrical buildings in elevation abrupt change in lateral resistance
Vertical strength discontinuities concentrate damage in the ldquosoftrdquo stories
Short column
Detailing concerns
Large tie spacing in columns lack of confinement of concrete core shear failures
Insufficient column lengths concrete to spall
Locations of inadequate splices brittle shear failure
Insufficient column strength for full moment hinge capacity brittle shear failure
Lack of continuous beam reinforcement hinge formation during load reversals
Inadequate reinforcing of beam column joints or location of beam bar splices at columns
joint failures
Improper bent-up of longitudinal reinforcing in beams as shear reinforcement shear failure
during load reversal
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Foundation dowels that are insufficient to develop the capacity of the column steel above
local column distress
(iii) Seismic Evaluation Data
Seismic evaluation of data will provide a general idea about the building performance during an
earthquake The criteria of evaluation of building will depend on materials strength and ductility
of structural components and detailing of reinforcement
Material Evaluation
Buildings height gt 3 stories minimum grade concrete M 20 desirable M 30 to M 40
particularly in columns of lower stories
Maximum grade of steel should be Fe 415 due to adequate ductility
No significant deterioration in reinforcement
No evidence of corrosion or spalling of concrete
Structural components
Evaluation of columns shear strength and drift check for permissible limits
Evaluation of plan irregularities check for torsional forces and concentration of forces
Evaluation of vertical irregularities check for soft storey mass or geometric discontinuities
Evaluation of beam-column joints check for strong column-weak beams
Evaluation of pounding check for drift control or building separation
Evaluation of interaction between frame and infill check for force distribution in frames and
overstressing of frames
(i) Flexural members
Limitation of sectional dimensions
Limitation on minimum and maximum flexural reinforcement at least two continuous
reinforced bars at top and bottom of the members
Restriction of lap splices
Development length requirements for longitudinal bars
Shear reinforcement requirements stirrup and tie hooks tie spacing bar splices
(ii) Columns
Limitation of sectional dimensions
Longitudinal reinforcement requirement
Transverse reinforcement requirements stirrup and tie hooks column tie spacing
column bar splices
Special confining requirements
(iii) Foundation
Column steel doweled into the foundation
Non-structural components
Cornices parapet and appendages are anchored
Exterior cladding and veneer are well anchored
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11112 Field Evaluation Visual Inspection Method
The procedure for visual inspection method is as below
Equipments
Optical magnification allows a detailed view of local areas of distress
Stereomicroscope that allow a three dimensional view of the surface Investigator can
estimate the elevation difference in surface features by calibrating the focus adjustment
screw
Fibrescope and borescopes allow inspection of regions that are inaccessible to the naked eye
Tape to measure the dimension of structure length of cracks
Flashlight to aid in lighting the area to be inspected particularly in post-earthquake
evaluation power failure
Crack comparator to measure the width of cracks at representative locations two types
plastic cards and magnifying lens comparators
Pencil to draw the sketch of cracks
Sketchpad to prepare a representation of wall elevation indicating the location of cracks
spalling or other damage records of significant features such as non-structural elements
Camera for photographs or video tape of the observed cracking
Action
Perform a walk through visual inspection to become familiar with the structure
Gather background documents and information on the design construction maintenance
and operation of structure
Plan the complete investigation
Perform a detailed visual inspection and observe type of damage cracks spalls and
delaminations permanent lateral displacement and buckling or fracture of reinforcement
estimating of drift
Observe damage documented on sketches interpreted to assess the behaviour during
earthquake
Perform any necessary sampling basis for further testing
Data Collection
To identify the location of vertical structural elements columns and walls
To sketch the elevation with sufficient details dimensions openings observed damage such
as cracks spalling and exposed reinforcing bars width of cracks
To take photographs of cracks use marker paint or chalk to highlight the fine cracks or
location of cracks in photographs
Observation of the non-structural elements inter-storey displacement
Limitations
Applicable for surface damage that can be visualised
No identification of inner damage health monitoring of building chang of frequency and
mode shapes
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11113 Non-destructive testing (NDT)
Visual inspection has the obvious limitation that only visible surface can be inspected Internal
defects go unnoticed and no quantitative information is obtained about the properties of the
concrete For these reasons a visual inspection is usually supplemented by NDT methods Other
detailed testing is then conducted to determine the extent and to establish causes
NDT tests for condition assessment of structures
Some methods of field and laboratory testing that may assess the minimum concrete strength and
condition and location of the reinforcement in order to characterize the strength safety and
integrity are
(i) Rebound hammer Swiss hammer
The rebound hammer is the most widely used non-destructive device for quick surveys to assess
the quality of concrete In 1948 Ernest Schmidt a Swiss engineer developed a device for testing
concrete based upon the rebound principal strength of in-place concrete comparison of concrete
strength in different locations and provides relative difference in strength only
Limitations
Not give a precise value of compressive strength provide estimate strength for comparison
Sensitive to the quality of concrete carbonation increases the rebound number
More reproducible results from formed surface rather than finished surface smooth hard-
towelled surface giving higher values than a rough-textured surface
Surface moisture and roughness also affect the reading a dry surface results in a higher
rebound number
Not take more than one reading at the same spot
(ii) Penetration resistance method ndash Windsor probe test
Penetration resistance methods are used to determine the quality and compressive strength of in-
situ concrete It is based on the determination of the depth of penetration of probes (steel rods or
pins) into concrete by means of power-actuated driver This provides a measure of the hardness
or penetration resistance of the material that can be related to its strength
Limitations
Both probe penetration and rebound hammer test provide means of estimating the relative
quality of concrete not absolute value of strength of concrete
Probe penetration results are more meaningful than the results of rebound hammer
Because of greater penetration in concrete the prove test results are influenced to a lesser
degree by surface moisture texture and carbonation effect
Probe test may be the cause of minor cracking in concrete
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(iii) Rebar locatorconvert meter
It is used to determine quantity location size and condition of reinforcing steel in concrete It is
also used for verifying the drawing and preparing as-built data if no previous information is
available These devices are based on interaction between the reinforcing bars and low frequency
electromagnetic fields Commercial convert meter can be divided into two classes those based
on the principal of magnetic reluctance and those based on eddy currents
Limitations
Difficult to interpret at heavy congestion of reinforcement or when depth of reinforcement is
too great
Embedded metals sometimes affect the reading
Used to detect the reinforcing bars closest to the face
(iv) Ultrasonic pulse velocity
It is used for determination the elastic constants (modulus of elasticity and Poissonrsquos ratio) and
the density By conducting tests at various points on a structure lower quality concrete can be
identified by its lower pulse velocity Pulse-velocity measurements can detect the presence of
voids of discontinuities within a wall however these measurements can not determine the depth
of voids
Limitations
Moisture content an increase in moisture content increases the pulse velocity
Presence of reinforcement oriented parallel to the pulse propagation direction the pulse may
propagate through the bars and result is an apparent pulse velocity that is higher than that
propagating through concrete
Presence of cracks and voids increases the length of the travel path and result in a longer
travel time
(v) Impact echo
Impact echo is a method for detecting discontinuities within the thickness of a wall An impact-
echo test system is composed of three components an impact source a receiving transducer and
a waveform analyzer or a portable computer with a data acquisition
Limitations
Accuracy of results highly dependent on the skill of the engineer and interpreting the results
The size type sensitivity and natural frequency of the transducer ability of FFT analyzer
also affect the results
Mainly used for concrete structures
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(vi) Spectral analysis of surface waves (SASW)
To assess the thickness and elastic stiffness of material size and location of discontinuities
within the wall such as voids large cracks and delimitations
Limitations
Interpretation of results is very complex
Mainly used on slab and other horizontal surface to determine the stiffness profiles of soil
sites and of flexible and rigid pavement systems measuring the changes in elastic properties
of concrete slab
(vii) Penetrating radar
It is used to detect the location of reinforcing bars cracks voids or other material discontinuities
verify thickness of concrete
Limitations
Mainly used for detecting subsurface condition of slab-on-grade
Not useful for detecting the small difference in materials
Not useful for detecting the size of bars closely spaced bars make difficult to detect features
below the layer of reinforcing steel
1112 ववशलषणमतरक िरीक ANALYTICAL METHODS
Analytical methods are based on considering capacity and ductility of the buildings which are
based on detailed dynamic analysis of buildings The methods in this category are
capacitydemand method pushover analysis inelastic time history analysis etc Brief discussions
on the method of evaluation are as follows
11121 CapacityDemand (CD) method
The forces and displacements resulting from an elastic analysis for design earthquake are
called demand
These are compared with the capacity of different members to resist these forces and
displacements
A (CD) ratio less than one indicate member failure and thus needs retrofitting
When the ductility is considered in the section the demand capacity ratio can be equated to
section ductility demand of 2 or 3
The main difficulty encountered in using this method is that there is no relationship between
member and structure ductility factor because of non-linear behaviour
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11122 Push Over Analysis
The push over analysis of a structure is a static non-linear analysis under permanent vertical
loads and gradually increasing lateral loads
The equivalent static lateral loads approximately represent earthquake-induced forces
A plot of total base shear verses top displacement in a structure is obtained by this analysis
that would indicate any premature failure or weakness
The analysis is carried out up to failure thus it enables determination of collapse load and
ductility capacity
On a building frame loaddisplacement is applied incrementally the formation of plastic
hinges stiffness degradation and plastic rotation is monitored and lateral inelastic force
versus displacement response for the complete structure is analytically computed
This type of analysis enables weakness in the structure to be identified The decision to
retrofit can be taken on the basis of such studies
11123 Inelastic time-history analysis
A seismically deficient building will be subjected to inelastic action during design earthquake
motion
The inelastic time history analysis of the building under strong ground motion brings out the
regions of weakness and ductility demand in the structure
This is the most rational method available for assessing building performance
There are computer programs available to perform this type of analysis
However there are complexities with regard to biaxial inelastic response of columns
modelling of joints behaviour interaction of flexural and shear strength and modelling of
degrading characteristics of member
The methodology is used to ascertain deficiency and post-elastic response under strong
ground shaking
Fig ndash 111 Strengthening strategies
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112 भवनो की रटरोफिट ग Retrofitting of Building
Retrofitting is to upgrade the strength and structural capacity of an existing structure to enable it
to safely withstand the effect of strong earthquakes in future
1121 सकटरचरल लवल यम गलोबल रटरोफि िरीक Structural Level or Global Retrofit
Methods
Two approaches are used for structural-level retrofitting
(i) Conventional Methods
(ii) Non-conventional methods
Retrofit procedure
Detailed seismic
evaluation
Retrofit
techniques
Seismic capacity
assessment
Selection of retrofit
scheme
Design of retrofit
scheme and detailing
Re-evaluation of
retrofit structure
Addition of infill walls
Addition of new
external walls
Addition of bracing
systems
Construction of wing
walls
Strengthening of
weak elements
Structural Level or Global Member Level or Local
Seismic Base Isolation
Jacketing of beams
Jacketing of columns
Jacketing of beam-
column joints
Strengthening of
individual footings
Seismic Dampers
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11211 Conventional Methods
Conventional Methods are based on increasing the seismic resistance of existing structure The
main categories of these methods are as follow
a) Addition of infilled walls
b) Addition of new external walls
c) Addition of bracing system
d) Construction of wing walls
e) Strengthening of weak elements
112111 Addition of infilled walls
The construction of infill walls within the frames of the load bearing structures as shown in the
example of Fig ndash 112 aims to drastically increase the strength and the stiffness of the structure
This method can also be applied in order to correct design errors in the structure and more
specifically when a large asymmetric distribution of strength or stiffness in elevation or an
eccentricity of stiffness in plan have been recognised
Fig - 112 Addition of infilled wall and wing walls
Fig - 113 Frames and shear wall
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As shown in Fig ndash 114 there are two alternatives methods of adding infill walls Either the infill
wall is simply placed between two existing columns or it is extended around the columns to form
a jacket The second method is specifically recommended in order to increase the strength in this
region In the situation where the existing columns are very weak a steel cage should be placed
around the columns before constructing new walls and column jackets In all cases the base of
any new wall should always be connected to the existing foundation
112112 Addition of new external walls
In some cases strengthening by adding concrete walls can be performed externally This can
often be carried out for functional reasons as for example in cases when the building must be
kept in operation during the intervention works New cast-in-place concrete walls constructed
outside the building can be designed to resist part or all the total seismic forces induced in the
building The new walls are preferably positioned adjacent to vertical elements (columns or
walls) of the building and are connected to the structure by placing special compression tensile
or shear connectors at every floor level of the building As shown in Figure 115 new walls
usually have a L-shaped cross-section and are constructed to be in contact with the external
corners of the building
Fig ndash 114 Two alternative methods of adding infill walls
Fig ndash 115 Schematic arrangement of connections between the existing building and
a new wall (a) plan (b) section of compression connector and (c) section of tension
connector
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It is important to ensure that connectors behave elastically under seismic design action effects
For this reason when designing the connectors a resistance safety factor equal to 14 is
recommended The use of compression and tensile connectors instead of shear connectors is
strongly recommended as much higher forces can be transferred It is essential that the anchorage
areas for the connectors on the existing
building and on the new walls have
enough strength to guarantee the transfer
of forces between new walls and the
existing structures
A very important issue of the above
method concerns the foundation of new
walls Foundation conditions should be
improved if large axial forces can be
induced in new walls during seismic
excitation In addition the construction
of short cantilever beams protruding from
the wall underneath the adjacent beams
at every floor level of the building as
shown in Fig ndash 116 appears to be a good solution
112113 Addition of bracing systems
The construction of bracing within
the frames of the load bearing
structure aims for a high increase
in the stiffness and a considerable
increase in the strength and
ductility of the structure Bracing
is normally constructed from steel
elements rather than reinforced
concrete as the elastic
deformation of steel aids the
absorption of seismic energy
Bracing systems can be used in a similar way as that for
steel constructions and can be applied easily in single-
storey industrial buildings with a soft storey ground floor
level where no or few brick masonry walls exist between
columns
Various truss configurations have been applied in
practice examples of which are K-shaped diamond
shaped or cross diagonal The latter is the most common
and is often the most effective solution
Fig ndash 116 Construction of cantilever beams to
transfer axial forces to new walls (a) plan (b)
section c-c
Fig ndash 117 Reinforced Concrete Building retrofitted
with steel bracing
Fig ndash 118 Steel bracing soft storey
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Use of steel bracing has a potential advantage over other schemes for the following reasons
Higher strength and stiffness can be proved
Opening for natural light can be
made easily
Amount of work is less since
foundation cost may be minimised
Bracing system adds much less
weight to the existing structure
Most of the retrofitting work can
be performed with prefabricated
elements and disturbance to the
occupants may be minimised
112114 Construction of wing wall
The construction of reinforced
concrete wing walls in continuous
connection with the existing columns
of a structure as shown above in
example of Fig ndash 112 is a very
popular technique
As presented in Fig ndash 1110 there are
two alternative methods of connecting
the wing wall to the existing load
bearing structure
In the first method the wall is connected to the column and the beams at the top and the base
of any floor level Steel dowels or special anchors are used for the connection and the
reinforcement of the new wall is welded to the existing reinforcement
In the second method the new wing wall is extended around the column to form a jacket
Obviously in this case stresses at the interface between the new concrete and the existing
column are considerably lower when compared to the first method
Moreover uncertainties regarding the capacity of the connection between the wall and the
column do not affect the seismic performance of the strengthened element Therefore the second
alternative method is strongly recommended
Fig ndash 1110 Construction of reinforced concrete wing
wall
Fig ndash 119 Steel bracing
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112115 Strengthening weak elements
The selective strengthening of weak elements of the
structure aims to avoid a premature failure of the critical
elements of a building and to increase the ductility of the
structure
Usually this method is applied to vertical elements and
is accompanied by the construction of fibre reinforced
polymer (FRP) jackets or as shown in Fig- 1111 steel
cages around the vertical elements
If a strength increase is also required this method can
include the construction of column jackets of shotcrete
or reinforced concrete
11212 Non-conventional methods
These are based on reduction of seismic demands Seismic demands are the force and
displacement resulting from an elastic analysis for earthquake design Incorporation of energy
absorbing systems to reduce seismic demands are as follows
(i) Seismic Base Isolation
(ii) Seismic Dampers
112121 Seismic Base Isolation
Isolation of
superstructure from the
foundation is known as
base isolation
It is the most powerful
tool for passive
structural vibration
control technique
Types of base isolations
Elastomeric Bearings
This is the most widely used Base Isolator
The elastomer is made of either Natural Rubber or Neoprene
The structure is decoupled from the horizontal components of the earthquake ground motion
Fig ndash 1111 Construction of a steel
cage around a vertical element
Fig ndash 1112 Base isolated structures
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Sliding System
a) Sliding Base Isolation Systems
It is the second basic type of isolators
This works by limiting the base shear across the
isolator interface
b) Spherical Sliding Base Isolators
The structure is supported by bearing pads that
have curved surface and low friction
During an earthquake the building is free to
slide on the bearings
c) Friction Pendulum Bearing
These are specially designed base isolators
which works on the
principle of simple
pendulum
It increases the natural time
period of oscillation by
causing the structure to
Fig ndash 1113 Elastomeric Isolators Fig ndash 1114 Steel Reinforced Elastomeric
Isolators
Fig ndash 1115 Metallic Roller Bearing
Fig ndash 1116 Spherical Sliding Base
Isolators
Fig ndash 1117 Cross-section of Friction Pendulum Bearing
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slide along the concave inner surface through the frictional interface
It also possesses a re-centering capability
Typically bearings measure 10 m (3 feet) in dia 200 mm (8 inches) in height and weight
being 2000 pounds
d) Advantages of base isolation
Isolate building from ground motion
Building can remain serviceable throughout construction
Lesser seismic loads hence lesser damage to the structure
Minimal repair of superstructure
Does not involve major intrusion upon existing superstructure
e) Disadvantages of base isolation
Expensive
Cannot be applied partially to structures unlike other retrofitting
Challenging to implement in an efficient manner
Allowance for building displacements
Inefficient for high rise buildings
Not suitable for buildings rested on soft soil
112122 Seismic Dampers
Seismic dampers are used in place of structural elements like diagonal braces for controlling
seismic damage in structures
It partly absorbs the seismic energy and reduces the motion of buildings
Types
Viscous Dampers Energy is absorbed by silicon-based fluid passing between piston-
cylinder arrangement
Fig -1118 Cross-section of a Viscous Fluid Damper
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Friction Dampers Energy is absorbed
by surfaces with friction between
rubbing against each other
Yielding Dampers Energy is absorbed
by metallic components that yield
1122 सदसकय सकिर यम सकथमनीय ररटरोफमइ िरीक Member Level or Local Retrofit Methods
The member level retrofit or local retrofit approach is to upgrade the strength of the members
which are seismically deficient This approach is more cost effective as compared to the
structural level retrofit
Jacketing
The most common method of enhancing the individual member strength is jacketing It includes
the addition of concrete steel or fibre reinforced polymer (FRP) jackets for use in confining
reinforced concrete columns beams joints and foundation
Types of jacketing
(1) Concrete jacketing (2) Steel jacketing (3) Strap jacketing
Fig ndash 1119 Friction Dampers
Fig ndash 1120 Yielding Dampers
Fig ndash 1121 Type of Jacketing
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11221 Member level Jacketing
(i) Jacketing of Columns
Different methods of column jacketing are as shown in Figures below
Fig ndash 1122 (b) Column with
CFRP (Carbon Fibre
Reinforced Polymer) Wrap
Fig ndash 1122 (c) Column with Steel Fig ndash 1122 (d) Column with
Jacketing Steel Caging
Fig ndash 1122 (a) Reinforced Concrete Jacketing
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Fig ndash 1122 (e) Construction techniques for Fig ndash 1122 (f) Local strengthening of RC
column jacketing Columns
Fig ndash 1122 (g) Details for provision of longitudinal reinforcement
Fig ndash 1122 (h) Different methods of column jacketing
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(ii) Jacketing of Beam
(iii) Jacketing of Beam-Column Joint
Fig ndash 1123 Different ways of beam jacketing
Fig ndash 1124 Continuity of longitudinal steel in jacketed beams
Fig ndash 1125 Steel cage assembled in the joint
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11222 Table showing the details of reinforced concrete jacketing
Properties of jackets match with the concrete of the existing structure
compressive strength greater than that of the existing
structures by 5 Nmm2 (50 kgcm
2) or at least equal to that
of the existing structure
Minimum width of
jacket 10 cm for concrete cast-in-place and 4 cm for shotcrete
If possible four sided jacket should be used
A monolithic behaviour of the composite column should be
assured
Narrow gap should be provided to prevent any possible
increase in flexural capacity
Minimum area of
longitudinal
reinforcement
3Afy where A is the area of contact in cm2 and fy is in
kgcm2
Spacing should not exceed six times of the width of the new
elements (the jacket in the case) up to the limit of 60 cm
Percentage of steel in the jacket with respect to the jacket
area should be limited between 0015 and 004
At least a 12 mm bar should be used at every corner for a
four sided jacket
Minimum area of
transverse
reinforcement
Designed and spaced as per earthquake design practice
Minimum bar diameter used for ties is not less than 10 mm
diameter anchorage
Due to the difficulty of manufacturing 135 degree hooks on
the field ties made up of multiple pieces can be used
Shear stress in the
interface Provide adequate shear transfer mechanism to assured
monolithic behaviour
A relative movement between both concrete interfaces
(between the jacket and the existing element) should be
prevented
Chipping the concrete cover of the original member and
roughening its surface may improve the bond between the
old and the new concrete
For four sided jacket the ties should be used to confine and
for shear reinforcement to the composite element
For 1 2 3 side jackets as shown in Figures special
reinforcement should be provided to enhance a monolithic
behaviour
Connectors Connectors should be anchored in both the concrete such that
it may develop at least 80 of their yielding stress
Distributed uniformly around the interface avoiding
concentration in specific locations
It is better to use reinforced bars (rebar) anchored with epoxy
resins of grouts as shown in Figure (a)
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11223 Practical aspects in choosing appropriate techniques
Certain issues of practical importance that may help to avoid mistakes in choosing the
appropriate technique are as follows
1) The strengthening of columns by using FRPs or steel jackets is unsuitable for flexible
structures where failure would be controlled by deflection In this case the strengthening
should aim to increase the stiffness
2) It is not favourable to use steel cages or confine with FRPs when an increase in the flexural
capacity of vertical elements is required
3) The application of confinement (with FRPs or steel) to circular or rectangular columns would
increase the ductility and the shear strength and would limit the slippage of overlapping bars
when the lap length has been found to be insufficient However a significant contribution
cannot be expected for columns of rectangular cross section with a large aspect ratio or those
with L-shaped cross sections
4) In the case of columns that have heavily rusted reinforcement strengthening with FRP
jackets (or the application of epoxy glue) will protect the reinforcement from further
oxidation However if the corrosion of the reinforcement is at an advanced stage it is
probable that strengthening may not stop the premature failure of the element
5) The construction of FRP jackets around vertical elements will increase the ductility but it
cannot increase the buckling resistance of the longitudinal reinforcement bars Thus if the
stirrups are too thin in an existing element failure will probably result from the premature
bending of the vertical reinforcement In this case local stress concentrations from the
distressed bars will build up between the stirrups and will lead to a local failure of the jacket
Consequently if bending of the vertical reinforcement has been evaluated as the most likely
cause of column failure the preferable choice for strengthening of the element would be to
place a steel cage
6) In areas where the overlapping of reinforcement bars has been found to be inadequate (short
lap lengths) confining the element with FRPs steel cages or steel jackets will improve the
strength and the ductility of the region considerably However even if it improved the
behaviour it is eventually unfeasible to deter the slipping of bars Consequently when the lap
length of bars has been found to be smaller than 30 of code requirements the solution of
welding of bars must be selected Moreover it must be pointed out that confinement cannot
offer anything to longitudinal bars that are not in the corners of the cross section
7) Experimentally the procedure of placing FRP sheets to strengthen weak beam-column joints
has proved to be particularly effective In practice however this technique has been found to
be difficult to apply due to the presence of slabs and transverse beams The same problems
arise when placing steel plates Other techniques such as the construction of reinforced
concrete jackets or the reconstruction of joints with additional interior reinforcement appear
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to be more beneficial In cases where only a light damage to the joints has been found
repairing with an epoxy resin appears to be particularly effective solution
8) The placing of new concrete in contact with an existing element (by shotcreting and
especially by pouring) will require prior aggravation of the old surface to a depth of at least 6
mm This should be performed by sandblasting or by using suitable mechanical equipment
(for example a scabbler and not just simply a hammer and a chisel) This is to remove the
exterior weak skin of the concrete and to expose the aggregate
9) When placing a new concrete jacket around an existing column it is not always possible to
follow code requirements and place
internal rectangular stirrups to enclose
the middle longitudinal bars as shown
in Fig-1126(a) In this case it is
proposed to place two middle bars in
each side of the jacket so that
octagonal stirrups can be easily
placed as demonstrated in
Fig-1126(b)
In the case where columns have a cross section
with a large aspect ratio the middle longitudinal
bars can be connected by drilling holes through
the section in order to place a S-shaped stirrup as
shown in Fig ndash 1127 After placing stirrups the
remaining void can be filled with epoxy resin In
order to ease placement the S-shaped stirrup can
be prefabricated with one hook and after placing
the second hook can be formed by hand
10) If a thin concrete jacket is to be
placed around a vertical element
and the 135 deg hooks at the ends
of the stirrups are impeded by the
old column it would be
acceptable to decrease the hook
anchorage from 10 times the bar
diameter to 5 or 6 times the bar
diameter as shown in
Fig ndash 1128(a) Otherwise the
ends the stirrups should be
welded together or connected
with special contacts (clamps) as
presented in Fig ndash 1128(b) that have now appeared on the market
(a) (b)
Fig ndash 1126 Placement of internal stirrups in
rectangular cross section
Fig ndash 1127 Placement of an internal
stirrup in a rectangular cross section
with a large aspect ratio
(a) (b)
Fig ndash 1128 Reducing hook lengths and welding the
ends of stirrups
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11) When constructing a jacket around a column it is
important to also strengthen the column joint As shown
in Fig ndash 1129 this can be accomplished by where
possible extending the longitudinal reinforcement bars
around the joint In addition as also shown in
Fig ndash 1129 stirrups must be placed in order to confine
the concrete of the jacket around the joint
In the case where the joint has been found to be
particularly weak a steel diagonal collar can be placed
around the joint before placing the reinforcement as
shown in Fig ndash 1130
12) It is preferable that a new concrete jacket is placed
continuously from the foundation to the top of the building
If this is not possible (due to maintaining the functioning of
the building) it is usual to stop the jacket at the top of the
ground floor level In this case there is a need to anchor the
jacketrsquos longitudinal bars to the existing column This can
be achieved by anchoring a steel plate to the base of the
column of the floor level above and then welding the
longitudinal bars to the anchor plate as shown in Fig ndash
1131
13) In the case where there is a need to reconstruct a heavily damaged column after first shoring
up the column all the defective concrete must be removed so that only good concrete
Fig ndash 1129 Strengthening the
column joint
Fig ndash 1130 Placing a steel diagonal collar
around a weak column joint
Fig ndash 1131 Removal of
defective concrete from a
heavily damaged column
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remains as shown in Fig ndash 1132 Any
buckled reinforcement bars must be welded
to the existing bars Finally the column can
be recast by placing a special non-shrink
concrete
14) In order to anchor new reinforcement bars dowels or anchors with the use of epoxy glue the
diameter of holes drilled into the existing concrete should be roughly 4 mm larger than the
diameter of the bar The best way to remove dust from drilled holes would be to spray water
at the back of the hole The best results (higher adhesive forces) are achieved when the walls
of the hole have been roughened slightly with a small wire brush
15) Care is required when shotcreting in the presence of reinforcement There is a danger of an
accumulation of material building up behind the bars This is usually accredited to material
sticking to the face of bars and may be due to either a low velocity a large firing distance or
insufficient pressure from the compressor
16) The placing of steel plates and especially FRP sheets or fabrics requires special preparation of
the concrete surface to which they will be stuck The rounding of corners and the removal of
surface abnormalities constitute minimal conditions for the application of this technique
17) Two constructional issues that concern the connection of new walls to the old frame require
particular attention The first problem is due to the shrinkage of the new concrete and the
appearance of cracks at the top of the new wall immediately below the old beam in the
region where a good contact between surfaces is essential Here the problem of shrinkage
can be usually dealt with by placing concrete of a particular composition where special
admixtures (for example expansive cements) have been used Alternatively the new wall
could be placed to about 20 cm below the existing beam and after more than 7 days (taking
into account temperature and how new concrete shrinks with time) the void can be filled
with an epoxy or polyster mortar In some cases depending on site conditions (ease of access
dry conditions etc) the new wall can be placed to a height of 2 to 5 mm below the beam and
the void filled with resin glue using the technique of resin injection The second problem
concerns the case of walls from ready-mix concrete and the difficulty of placing the higher
part of the wall due to insufficient access For this reason alone the use of shotcrete should
be the preferred option
Fig ndash 1132 Welding longitudinal bars to an
anchor plate
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113 आरसी भवनो क घ को र समरमनय भकपी कषतियम और उनक उपचमर Common
seismic damage in components of RC Buildings and their remedies
Possible damages in component of RC Buildings which are frequently observed after the
earthquakes are as follows
(i) R C Column
The most common modes of failure of column are as follows
Mode -1 Formation of plastic hinge at the base of ground level columns
Mechanism The column when subjected to seismic
motion its concrete begins to disintegrate and the
load carried by the concrete shifts to longitudinal
reinforcement of the column This additional load
causes buckling of longitudinal reinforcement As a
result the column shortens and looses its ability to
carry even the gravity load
Reasons Insufficient confinement length and
improper confinement in plastic hinge region due to
smaller numbers of ties
Remedies This type of damage is sensitive to the cyclic moments generated during the
earthquake and axial load intensity Consideration is to be paid on plastic hinge length or length
of confinement
Mode ndash 2 Diagonal shear cracking in mid span of columns
Mechanism In older reinforced
concrete building frames column
failures were more frequent since
the strength of beams in such
constructions was kept higher than
that of the columns This shear
failure brings forth loss of axial
load carrying capacity of the
column As the axial capacity
diminishes the gravity loads carried by the column are transferred to neighbouring elements
resulting in massive internal redistribution of forces which is also amplified by dynamic effects
causing spectacular collapse of building
Reason Wide spacing of transverse reinforcement
Remedies To improve understanding of shear strength as well as to understand how the gravity
loads will be supported after a column fails in shear
Fig ndash 1133 Formation of plastic hinge at
the base
Fig ndash 1134 Diagonal shear cracking in mid span of
columns
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Mode ndash 3 Shear and splice failure of longitudinal reinforcement
Mechanism Splices of column
longitudinal reinforcement in
older buildings were
commonly designed for
compression only with
relatively light transverse
reinforcement enclosing the
lap
Under earthquake motion the
longitudinal reinforcement may
be subjected to significant tensile stresses which require lap lengths for tension substantially
exceeding those for compression As a result slip occurs along the splice length with spalling of
concrete
Reasons Deficient lap splices length of column longitudinal reinforcement with lightly spaced
transverse reinforcement particularly if the splices just above the floor slab especially the splices
just above the floor slab which is very common in older construction
Remedies Lap splices should be provided only in the center half of the member length and it
should be proportionate to tension splice Spacing of transverse reinforcement as per IS
139291993
Mode ndash 4 Shear failures in captive columns and short columns
Captive column Column whose deforming ability is restricted and only a fraction of its height
can deform laterally It is due to presence of adjoining non-structural elements columns at
slopping ground partially buried basements etc
Fig - 1135 Shear and splice failure of longitudinal
reinforcement
Fig ndash 1136 Restriction to the Lateral
Displacement of a Column Creating a Captive-
Column Effect
Fig ndash 1137 Captive-column effect in a
building on sloping terrain
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A captive column is full storey slender column whose clear height is reduced by its part-height
contact with a relatively stiff non-structural element such as a masonry infill wall which
constraints its lateral deformation over
the height of contract
The captive column effect is caused by
a non-intended modification to the
original structural configuration of the
column that restricts the ability of the
column to deform laterally by partially
confining it with building components
The column is kept ldquocaptiverdquo by these
components and only a fraction of its
height can deform laterally
corresponding to the ldquofreerdquo portion
thus the term captive column Figure
as given below shows this situation
Short column Column is made shorter than neighbouring column by horizontal structural
elements such as beams girder stair way landing slabs use of grade beams and ramps
Fig ndash 1138 Typical captive-column failure Fig ndash 1139 Column damage due to
captive- column effect
Fig ndash 1140 Captive column caused by ventilation
openings in a partially buried basement
Fig ndash 1141 Short column created by
a stairway landing
Fig ndash 1142 Shear failures in captive columns
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For split-level buildings in order to circumvent the short-column effect the architect should
avoid locating a frame at the vertical plane where the transition between levels occurs For
buildings on slopes special care should be exercised to locate the sloping retaining walls in such
a way that no captive-column effects are induced Where stiff non-structural walls are still
employed these walls should be separated from the structure and in no case can they be
interrupted before reaching the full height of the adjoining columns
Mechanism A reduction in the clear height of captive or short columns increases the lateral
stiffness Therefore these columns are subjected to larger shear force during the earthquake since
the storey shear is distributed in proportion to lateral stiffness of the same floor If these columns
reinforced with conventional longitudinal and transverse reinforcement and subjected to
relatively high axial loading fail by splitting of concrete along their diagonals if the axial
loading level is low the most probable mode of failure is by shear sliding along full depth cracks
at the member ends Moreover in the case of captive column is so effective that usually damage
is shifted to the short non-confined upper section of the column
Reasons Large shear stresses when the structure is subjected to lateral forces are not accounted
for in the standard frame design procedure
Remedies The best solution for captive column or short column is to avoid the situation
otherwise use separation gap in between the non-structural elements and vertical structural
element with appropriate measures against out-of-plane stability of the masonry wall
(ii) R C Beams
The shear-flexure mode of failure is most commonly observed during the earthquakes which is
described as below
Mode ndash 5 Shear-flexure failure
Mechanism Two types of plastic hinges may form in the beams of multi-storied framed
construction depending upon the span of
beams In case of short beams or where
gravity load supported by the beam is
low plastic hinges are formed at the
column ends and damage occurs in the
form of opening of a crack at the end of
beam otherwise there is formation of
plastic hinges at and near end region of
beam in the form of diagonal shear
cracking
Reasons Lack of longitudinal compressive reinforcement infrequent transverse reinforcement in
plastic hinge zone bad anchorage of the bottom reinforcement in to the support or dip of the
longitudinal beam reinforcement bottom steel termination at face of column
Fig ndash 1143 Shear-flexure failure
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Remedies Adequate flexural and shear strength must be provided and verification by design
calculation is essential The beams should not be too stiff with respect to adjacent columns so
that the plastic hinging will occur in beam rather than in column To ensure that the plastic hinges
zones in beams have adequate ductility the following considerations must be considered
Lower and upper limits on the amount of longitudinal flexural tension steel
A limit on the ration of the steel on one side of the beam to that of on the other side
Minimum requirements for the spacing and size of stirrups to restrain buckling of the
longitudinal reinforcement
(iii) R C Beam-Column Joints
The most common modes of failure in beam-column joint are as follows
Mode ndash 6 shear failure in beam-column joint
Mechanism The most common
failure observed in exterior joints are
due to either high shear or bond
(anchorage) under severe
earthquakes Plastic hinges are
formed in the beams at the column
faces As a result cracks develop
throughout the overall beam depth
Bond deterioration near the face of
the column causes propagation of
beam reinforcement yielding in the joint and a shortening of the bar length available for force
transfer by bond causing horizontal bar slippage in the joint In the interior joint the beam
reinforcement at both the column faces undergoes different stress conditions (compression and
tension) because of opposite sights of seismic bending moments results in failure of joint core
Reasons Inadequate anchorage of flexural steel in beams lack of transverse reinforcement
Remedies Exterior Joint ndash The provision on anchorage stub for the beam reinforcement
improves the performance of external joints by preventing spalling of concrete cover on the
outside face resulting in loss of flexural strength of the column This increases diagonal strut
action as well as reduces steel congestion as the beam bars can be anchored clear of the column
bars
(iv) R C Slab
Generally slab on beams performed well during earthquakes and are not dangerous but cracks in
slab creates serious aesthetic and functional problems It reduces the available strength stiffness
and energy dissipation capacity of building for future earthquake In flat slab construction
punching shear is the primary cause of failure The common modes of failure are
Fig - 1144 Shear failure in beam-column joint
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Mode ndash 7 Shear cracking in slabs
Mechanism Damage to slab oftenly
occurs due to irregularities such as large
openings at concentration of earthquake
forces close to widely spaced shear
walls at the staircase flight landings
Reasons Existing micro cracks which
widen due to shaking differential
settlement
Remedies
Use secondary reinforcement in the bottom of the slab
Avoid the use of flat slab in high seismic zones provided this is done in conjunction with a
stiff lateral load resisting system
(v) R C Shear Walls
Shear walls generally performed well during the earthquakes Four types of failure modes are
generally observed
Mode ndash 8 Four types of failure modes are generally observed
(i) Diagonal tension-compression failure in the form of cross-shaped shear cracking
(ii) Sliding shear failure cracking at interface of new and old concrete
(iii) Flexure and compression in bottom end region of wall and finally
(iv) Diagonal tension in the form of X shaped cracking in coupling beams
Fig ndash 1145 Shear cracking in slabs
Fig ndash 1146 Diagonal tension-compression Sliding shear Flexure and compression
failure
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Mechanism Shear walls are subjected to shear and flexural deformation depending upon the
slenderness ratio Therefore the damage in shear walls may generally occurs due to inadequate
shear and flexure capacity of wall Slender walls are governed by their flexural strength and
cracking occurs in the form of yielding of main flexure reinforcement in the plastic hinge region
normally at the base of the wall Squat walls are governed by their shear strength and failure
takes place due to diagonal tension or diagonal compression in the form of inclined cracking
Coupling beams between shear walls or piers may also damage due to inadequate shear and
flexure capacity Sometimes damage occurs at the construction joints in the form of slippage and
related drift
Reasons
Flexuralboundary compression failure Inadequate transverse confining reinforcement to the
main flexural reinforcement near the outer edge of wall in boundary elements
Flexurediagonal tension Inadequate horizontal shear reinforcement
Sliding shear Absence of diagonal reinforcement across the potential sliding planes of the
plastic hinge zone
Coupling beams Inadequate stirrup reinforcement and no diagonal reinforcement
Construction joint Improper bonding between two surfaces
Remedies
The concrete shear walls must have boundary elements or columns thicker than walls which
will carry the vertical load after shear failure of wall
A proper connection between wall versus diaphragm as well as wall versus foundation to
complete the load path
Proper bonding at construction joint in the form of shear friction reinforcement
Provision of diagonal steel in the coupling beam
Fig ndash 1147 Diagonal tension in the form of X shaped
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(v) Infill Walls
Infill panels in reinforced concrete frames are the cause of unequal distribution of lateral forces
in the different frames of a building producing vertical and horizontal irregularities etc the
common mode of failure of infill masonry are in plane or shear failure
Mode ndash 9 Shear failure of masonry infill
Mechanism Frame with infill possesses much more lateral stiffness than the bare frame and
hence initially attracts most of the lateral force during an earthquake Being brittle the infill
starts to disintegrate as soon as its strength is reached Infills that were not adequately tied to the
surrounding frames sometimes dislodges by out-of-plane seismic excitations
Reasons Infill causes asymmetry of load application resulting in increased torsional forces and
changes in the distribution of shear forces between lateral load resisting system
Remedies Two strategies are possible either complete separation between infill walls and frame
by providing separation joint so that the two systems do not interact or complete anchoring
between frame and infill to act as an integral unit Horizontal and vertical reinforcement may also
be used to improve the strength stiffness and deformability of masonry infill walls
(vi) Parapets
Un-reinforced concrete parapets with large height-to-thickness ratio and not in proper anchoring
to the roof diaphragm may also constitute a hazard The hazard posed by a parapet increases in
direct proportion to its height above building base which has been generally observed
The common mode of failure of parapet wall is against out-of-plane forces which is described as
follows
Mode ndash 10 Brittle flexure out-of-plane failure
Mechanism Parapet walls are acceleration sensitive in the out-of-plane direction the result is
that they may become disengaged and topple
Fig ndash 1148 Shear failure of masonry infill
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141
Reasons Not properly braced
Remedies Analysed for acceleration forces and braced and connected with roof diaphragm
114 चचनमई सरचनमओ की रटरोफिट ग Retrofitting of Masonry Structures
(a) Principle of Seismic Safety of Masonry Buildings
Integral box action
Integrity of various components
- Roof to wall
- Wall to wall at corners
- Wall to foundation
Limit on openings
(b) Methods for Retrofitting of Masonry Buildings
Repairing (Improving existing masonry strength)
Stitching of cracks
Grouting with cement or epoxy
Use of CFRP (Carbon Fibre Reinforced Polymer) strips
Fig ndash 1149 Brittle flexure out-of-plane failure
(a) (b)
Fig ndash 1150 (a) Stitching of cracks Fig ndash 1150 (b) Repair of damaged member in
masonry walls
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(c) Retrofitting of Earthquake vulnerable buildings
External binding or jacketing
Shotcreting
Strengthening of wall intersections
Strengthening by cross wall
Strengthening by buttresses
Strengthening of arches
Fig ndash 1151 Integral Box action
(a) (b)
Fig - 1152 (a) Strengthening of Wall Fig - 1152 (b) Strengthening by
intersections cross wall
(a) (b)
Fig ndash 1153 (a) Strengthening by Fig ndash 1153 (b) Strengthening of Arches
Buttresses
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पररलिष Annexure ndash I
भारिीय भको पी सोतििाएा Indian Seismic Codes
Development of building codes in India started rather early Today India has a fairly good range
of seismic codes covering a variety of structures ranging from mud or low strength masonry
houses to modern buildings However the key to ensuring earthquake safety lies in having a
robust mechanism that enforces and implements these design code provisions in actual
constructions
भको पी तिजाइन कोि का मितव Importance of Seismic Design Codes
Ground vibrations during earthquakes cause forces and deformations in structures Structures
need to be designed to withstand such forces and deformations Seismic codes help to improve
the behaviour of structures so that they may withstand the earthquake effects without significant
loss of life and property An earthquake-resistant building has four virtues in it namely
(a) Good Structural Configuration Its size shape and structural system carrying loads are such
that they ensure a direct and smooth flow of inertia forces to the ground
(b) Lateral Strength The maximum lateral (horizontal) force that it can resist is such that the
damage induced in it does not result in collapse
(c) Adequate Stiffness Its lateral load resisting system is such that the earthquake-induced
deformations in it do not damage its contents under low-to moderate shaking
(d) Good Ductility Its capacity to undergo large deformations under severe earthquake shaking
even after yielding is improved by favourable design and detailing strategies
Seismic codes cover all these aspects
भारिीय भको पी सोतििाएा Indian Seismic Codes
Seismic codes are unique to a particular region or country They take into account the local
seismology accepted level of seismic risk building typologies and materials and methods used
in construction The first formal seismic code in India namely IS 1893 was published in 1962
Today the Bureau of Indian Standards (BIS) has the following seismic codes
1 IS 1893 (Part I) 2002 Indian Standard Criteria for Earthquake Resistant Design of
Structures (5 Revision)
2 IS 4326 1993 Indian Standard Code of Practice for Earthquake Resistant Design and
Construction of Buildings (2nd Revision)
3 IS 13827 1993 Indian Standard Guidelines for Improving Earthquake Resistance of
Earthen Buildings
4 IS 13828 1993 Indian Standard Guidelines for Improving Earthquake Resistance of Low
Strength Masonry Buildings
5 IS 13920 1993 Indian Standard Code of Practice for Ductile Detailing of Reinforced
Concrete Structures Subjected to Seismic Forces
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6 IS 13935 1993 Indian Standard Guidelines for Repair and Seismic Strengthening of
Buildings
The regulations in these standards do not ensure that structures suffer no damage during
earthquake of all magnitudes But to the extent possible they ensure that structures are able to
respond to earthquake shakings of moderate intensities without structural damage and of heavy
intensities without total collapse
IS 1893 (Part I) 2002
IS 1893 is the main code that provides the seismic zone map and specifies seismic design force
This force depends on the mass and seismic coefficient of the structure the latter in turn
depends on properties like seismic zone in which structure lies importance of the structure its
stiffness the soil on which it rests and its ductility For example a building in Bhuj will have
225 times the seismic design force of an identical building in Bombay Similarly the seismic
coefficient for a single-storey building may have 25 times that of a 15-storey building
The revised 2002 edition Part 1 of IS1893 contains provisions that are general in nature and
those applicable for buildings The other four parts of IS 1893 will cover
a) Liquid-Retaining Tanks both elevated and ground supported (Part 2)
b) Bridges and Retaining Walls (Part 3)
c) Industrial Structures including Stack Like Structures (Part 4) and
d) Dams and Embankments (Part 5)
These four documents are under preparation In contrast the 1984 edition of IS1893 had
provisions for all the above structures in a single document
Provisions for Bridges
Seismic design of bridges in India is covered in three codes namely IS 1893 (1984) from the
BIS IRC 6 (2000) from the Indian Roads Congress and Bridge Rules (1964) from the Ministry
of Railways All highway bridges are required to comply with IRC 6 and all railway bridges
with Bridge Rules These three codes are conceptually the same even though there are some
differences in their implementation After the 2001 Bhuj earthquake in 2002 the IRC released
interim provisions that make significant improvements to the IRC6 (2000) seismic provisions
IS 4326 1993 (Reaffirmed 2003)
This code covers general principles for earthquake resistant buildings Selection of materials
and special features of design and construction are dealt with for the following types of
buildings timber constructions masonry constructions using rectangular masonry units and
buildings with prefabricated reinforced concrete roofingflooring elements The code
incorporates Amendment No 3 (January 2005)
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IS 13827 1993 and IS 13828 1993
Guidelines in IS 13827 deal with empirical design and construction aspects for improving
earthquake resistance of earthen houses and those in IS 13828 with general principles of
design and special construction features for improving earthquake resistance of buildings of
low-strength masonry This Masonry includes burnt clay brick or stone masonry in weak
mortars like clay-mud These standards are applicable in seismic zones III IV and V
Constructions based on them are termed non-engineered and are not totally free from collapse
under seismic shaking intensities VIII (MMI) and higher Inclusion of features mentioned in
these guidelines may only enhance the seismic resistance and reduce chances of collapse
IS 13920 1993 (Reaffirmed 2003)
In India reinforced concrete structures are designed and detailed as per the Indian Code IS 456
(2002) However structures located in high seismic regions require ductile design and
detailing Provisions for the ductile detailing of monolithic reinforced concrete frame and shear
wall structures are specified in IS 13920 (1993) After the 2001 Bhuj earthquake this code has
been made mandatory for all structures in zones III IV and V Similar provisions for seismic
design and ductile detailing of steel structures are not yet available in the Indian codes
IS 13935 1993
These guidelines cover general principles of seismic strengthening selection of materials and
techniques for repairseismic strengthening of masonry and wooden buildings The code
provides a brief coverage for individual reinforced concrete members in such buildings but
does not cover reinforced concrete frame or shear wall buildings as a whole Some guidelines
are also laid down for non-structural and architectural components of buildings
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पररलिष Annexure ndash II
Checklist Multiple Choice Questions for Points to be kept in mind during
Construction of Earthquake Resistant Building
S No Description Observer Remarks
1 Seismic Zone in which building is located
i) Zone II ndash Least Seismically Prone Region
ii) Zone III ndash
iii) Zone IV ndash
iv) Zone V ndash Most Seismically Prone Region
Choose Zone
2 Environment condition to which building is exposed
a) Mild b) Moderate c) Severe d) Very Severe e) Extreme
Choose Condition
3 Whether the building is located in Flood Zone YesNo
4 Whether the building is located in Land Slide Zone ie building is on
hill slope or Plane Area
YesNo
5 Type of soil at founding level
a) Rock or Hard Soil
b) Medium Soil
c) Soft Soil
Choose type of soil
6 Type of Building
I) Load Bearing Masonry Building
a) Brick Masonry Construction
b) Stone Masonry construction
II) RCC Framed Structure
a) Regular frame
b) Regular Frame with shear wall
c) Irregular Frame
d) Irregular Frame with shear wall
e) Soft Story Building
Choose type of
building
7 No of Story above Ground Level with provision of Future Extension Mention Storey
8 Category of Building considering Seismic Zone and Importance
Factor (As per Table ndash 102)
i) Category B ndash Building in Seismic Zone II with Importance Factor
10
ii) Category E- Building in Seismic Zone II with Importance Factor
10 and 150
Choose category
9 Bricks should not have compressive strength less than 350 MPa YesNo
10 Minimum wall thickness of brick masonry
i) 1 Brick ndash Single Storey Construction
ii) 1 frac12 Brick ndash In bottom storey up to 3 storey construction amp
1 Brick in top storey with brick masonry
Choose appropriate
11 Height of building is restricted to
i) For A B amp C categories ndash G+2 with flat roof G+1 plus anti for
pitched roof when height of each story not exceed 3 m
ii) D category ndash G+1 with flat Roof
- Ground plus attic for pitched roof
Choose appropriate
12 Max Height of Brick masonry Building ndash 15 m (max 4 storey) YesNo
13 Mortar mix shall be as per Table ndash 102 for category A to E Choose Mortar
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14 Height of Stone Masonry wall
i) For Categories AampB ndash
a) When built in Lime-Sand or Mud mortar
ndash Two storey with flat roof or One Storey plus attic
b) When build in cement sand 16 mortar
- One story higher
ii) For Categories CampD ndash
a) When built in cement Sand 16 Mortar
- Two storey with flat roof or One Storey plus attic for pitched
roof
b) When build in lime sand or Mud mortar
- One story with flat roof or One Story plus attic
Choose appropriate
15 Through stone at full length equal to wall thickness in every 600 mm
lift at not more than 120 m apart horizontally has been provided
YesNo
16 Through stone and Bond Element as per Fig 1024 has been provided YesNo
17 Horizontal Bands
a) Plinth Band
b) Lintel Band
c) Roof Bond
d) Gable Bond
For Over Strengthening Arrangement for Category D amp E Building
have been provided
YesNo
18 Bond shall be made up of Reinforced Concrete of Grade not leaner
than M15 or Reinforced brick work in cement mortar not leaner than
13
YesNo
19 Bond shall be of full width of wall not less than 75 mm in depth and
reinforced with steel as shown in Table ndash 106
YesNo
20 Vertical steel at corners amp junction of wall which are up to 340 mm
(1 frac12 brick) thick shall be provided as shown in Table ndash 101
YesNo
21 General principal for planning building are
i) Building should be as light as possible
ii) All parts of building should be tied together to act as one unit
iii) Projecting part should be avoided
iv) Building having plans with shape L T E and Y shall preferably
be separated in to rectangular parts
v) Structure not to be founded on loose soil which will subside or
liquefy during Earthquake resulting in large differential
settlement
vi) Heavy roofing material should be avoided
vii) Large stair hall shall be separated from Rest of the Building by
means of separation or crumple section
viii) All of the above
ix) None of the above
Choose Correct
22 Structural irregularities may be
i) Horizontal Irregularities
ii) Vertical Irregularities
iii) All of the above
iv) None of the above
Choose Correct
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23 Horizontal Irregularities are
i) Asymmetrical plan shape (eg LTUF)
ii) Horizontal resisting elements (diaphragms)
iii) All of the above
iv) None of the above
Choose Correct
24 Horizontal Irregularities result in
i) Torsion
ii) Diaphragm deformation
iii) Stress Concentration
iv) All of the above
v) None of the above
Choose Correct
25 Vertical Irregularities are
i) Sudden change of stiffness over height of building
ii) Sudden change of strength over height of building
iii) Sudden change of geometry over height of building
iv) Sudden change of mass over height of building
v) All of the above
vi) None of the above
Choose Correct
26 Soft story in one
i) Which has lateral stiffness lt 70 of story above
ii) Which has lateral stiffness lt 80 of average lateral stiffness of 3
storeys above
iii)All of the above
vi) None of the above
Choose Correct
27 Extreme soft storey in one
i) Which has lateral stiffness lt 60 of storey above
ii) Which has lateral stiffness lt 70 of average lateral stiffness of 3
storeys above
iii)All of the above
iv)None of the above
Choose Correct
28 Weak Storey is one
i) Which has lateral strength lt 80 of storey above
ii) Which has lateral strength lt 80 of storey above
iii)All of the above
iv)None of the above
Choose Correct
29 Natural Period of Building
It is the time taken by the building to undergo one complete
cycle of oscillation during shaking
True False
30 Fundamental Natural Period of Building
Natural period with smallest Natural Frequency ie with largest
natural period is called Fundamental Natural Period
True False
31
Type of building frame system
i) Ordinary RC Moment Resisting Frame (OMRF)
ii) Special RC Moment Resisting Frame (SMRF)
iii) Ordinary Shear Wall with OMRF
iv) Ordinary Shear Wall with SMRF
v) Ductile Shear wall with OMRF
vi) Ductile Shear wall with SMRF
vii) All of the above
Choose Correct
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32 Zone factor to be considered for
i) Zone II ndash 010
ii) Zone III ndash 016
iii) Zone IV ndash 024
iv) Zone V ndash 036
True False
33 Importance Factor
i) Important building like school hospital railway station 15
ii) All other buildings 10
True False
34 Design of Earthquake effect is termed as
i) Earthquake Proof Design
or
ii) Earthquake Resistant Design
Choose Correct
35 Seismic Analysis is carried out by
i) Dynamic analysis procedure [Clause 78 of IS1893 (Part I) 2002]
ii) Simplified method referred as Lateral Force Procedure [Clause
75 of IS 1893 (Part I) 2002]
True False
36 Dynamic Analysis is performed for following buildings
(a) Regular Building gt 40 m height in Zone IV amp V
gt 90 height in Zone II amp III
(b) Irregular Building
gt 12 m all framed building in Zone IV amp V
gt 40 m all framed building in Zone II and III
True False
37 Base Shear for Lateral Force Procedure is
VB = Ah W =
True False
38 Distribution of Base Shear to different Floor level is
True False
39 Concept of capacity design is to
Ensure that brittle element will remain elastic at all loads prior to
failure of ductile element
True False
40 lsquoStrong Column ndash Weak Beamrsquo Philosophy is
For a building to remain safe during Earthquake shacking columns
should be stronger than beams and foundation should be stronger
than columns
True False
41 Rigid Diaphragm Action is
Geometric distortion of Slab in horizontal plane under influence of
horizontal Earthquake force is negligible This behaviour is known
as Rigid Diaphragm Action
True False
42 Soft storied buildings are
Column on Ground Storey do not have infill walls (of either
masonry or RC)
True False
43 Soft Storey or Open Ground Story is also termed as weak storey True False
44 Short columns in building suffer significant damage during an earth-
quake
True False
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45 Building can be protected from damage due to Earthquake effect by
using
a) Base Isolation Devices
b) Seismic Dampers
True False
46 Idea behind Base Isolation is
To detach building from Ground so that EQ motion are not
transmitted through the building or at least greatly reduced
True False
47 Base Isolation is done through
Flexible Pads connected to building and foundation True False
48 Seismic Dampers are
(i) Special devices to absorb the energy provided by Ground Motion
to the building
(ii) They act like hydraulic shock absorber in cars
True False
49 Commonly used Seismic Dampers are
(i) Viscous Dampers
(ii) Friction Dampers
(iii) Yielding Dampers
True False
50 For Ductility Requirement
(i) Min Grade of Concrete shall be M20 for all buildings having
more than 3 storeys in height
(ii) Steel Reinforcement of Grade Fe 415 or less only shall be used
(iii) Grade Fe 500 amp Fe 550 having elongation more than 145 may
be used
True False
51 For Ductility Requirement Flexure Members shall satisfy the
following requirement
(i) width of member shall not be less than 200 mm
(ii) width to depth ratio gt 03
(iii) depth of member D lt 14th of clear span
(iv) Factored Axial Stress on the member under Earthquake loading
shall not be greater than 01 fck
True False
52 For Ductility Requirement Longitudinal reinforcement in Flexure
Member shall satisfy the following requirements
i) Top and bottom reinforcement consist of at least 2 bars
throughout member length
ii) Tensile Steel Ratio on any face at any section shall not be less
than ρmin = (024 radic fck) fy
iii) Max Steel ratio on any face at any section shall not exceed
ρmax = 0025
iv) + ve steel at Joint face must be at least equal to half the ndashve steel
at that face
v) Steel provided at each of the top amp bottom face of the member
at any section along its length shall be at least equal to 14th of
max ndashve moment steel provided at the face of either joint
True False
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(vi) Detailing of Reinforcement at Beam-Column Joint
(vii) Detailing of Splicing
53 For Ductile Requirement in compression member
i) Minimum diversion of member shall not be less than 200 mm
ii) In Frames with beams cc Span gt 5m or
unsupported length of column gt 4 m shortest dimension shall not
be less than 300 mm
iii) Ratio of shortest cross sectional dimension to the perpendicular
dimension shall probably not less than 04
True False
54 For Ductile Requirement Longitudinal reinforcement in compression
member shall satisfy the following requirements
i) Lap splice shall be provided only in the central half of the member
length proportional as tension splice
ii) Hoop shall be provided over entire splice length at spacing not
greater than 150 mm
iii) Not more than 50 bar shall be spliced at one section
True False
55 When a column terminates into a footing or mat special confining
reinforcement shall extend at least 300 mm into the footing or mat
True False
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सोदभयगरोथ सची BIBLIOGRAPHY
1 Guidelines for Earthquake Resistant Non-Engineered Construction reprinted by
Indian Institute of Technology Kanpur 208016 India (Source wwwniceeorg)
2 IS 1893 (Part 1) 2002 Criteria for Earthquake Resistant Design Of Structures
PART- 1 GENERAL PROVISIONS AND BUILDINGS (Fifth Revision )
3
IS 4326 1993 (Reaffirmed 1998) Edition 32 (2002-04) Earthquake Resistant
Design and Construction of Buildings ndash Code of Practice ( Second Revision )
(Incorporating Amendment Nos 1 amp 2)
4 IS 13828 1993 (Reaffirmed 1998) Improving Earthquake Resistance of Low
Strength Masonry Buildings ndash Guidelines
5
IS 13920 1993 (Reaffirmed 1998) Edition 12 (2002-03) Ductile Detailing of
Reinforced Concrete Structures subjected to Seismic Forces ndash Code of Practice
(Incorporating Amendment Nos 1 amp 2)
6 IS 13935 1993 (Reaffirmed 1998) Edition 11 (2002-04) Repair and Seismic
Strengthening of Buildings ndash Guidelines (Incorporating Amendment No 1)
7
Earthquake Tips authored by Prof C V R Murty IIT Kanpur and sponsored by
Building Materials and Technology Promotion Council New Delhi India
(Source www wwwiitkacin)
8
Earthquake Engineering Practice Volume 1 Issue 1 March 2007 published by
National Information Center of Earthquake Engineering IIT Kanpur Kanpur
208016
9 Earthquake Resistant Design of Structures by Pankaj Agarwal and Manish
Shrikhande published by PHI Learning Private Limited Delhi 110092 (2015)
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तटपपणी NOTES
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तटपपणी NOTES
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हमारा उददशय
अनरकषि परौधौधगकी और कायापरिाली को उननयन करना तथा उतपादकता और
रलव की पररसमपवियो एव िनशजतत क ननषपादन म सधार करना जिसस
अतववाियो म ववशवसनीयता उपयोधगता और दकषता परापत की िा सकA
Our Objective
To upgrade Maintenance Technologies and Methodologies and achieve
improvement in productivity and performance of all Railway assets and
manpower which inter-alia would cover Reliability Availability and
Utilisation
तिसलमर Disclaimer
The document prepared by CAMTECH is meant for the dissemination of the knowledge information
mentioned herein to the field staff of Indian Railways The contents of this handbookbooklet are only for
guidance Most of the data amp information contained herein in the form of numerical values are indicative
and based on codes and teststrials conducted by various agencies generally believed to be reliable While
reasonable care and effort has been taken to ensure that information given is at the time believed to be fare
and correct and opinion based thereupon are reasonable Due to very nature of research it can not be
represented that it is accurate or complete and it should not be relied upon as such The readeruser is
supposed to refer the relevant codes manuals available on the subject before actual implementation in the
field
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Hkkjrh jsy jkrdquoV ordf dh thou js[kk ---hellip
INDIAN RAILWAYS Lifeline to the nation hellip
If you have any suggestion amp comments please write to us
Contact person Joint Director (Civil)
Phone (0751) - 2470869
Fax (0751) ndash 2470841
Email dircivilcamtechgmailcom
Charbagh Railway Station Lucknow
FOREWORD
The recent earthquakes occurred in many parts of world has caused considerable damage
to the buildings and lives The most dangerous building construction from an
earthquake point of view is unreinforced brick or concrete block Most houses of upto
four storeys are built of burnt clay brick masonry with reinforced concrete slabs
Similarly many new four or five storey reinforced concrete frame building being
constructed in small and large towns lack a proper frame system
With the recent earthquakes the discussion on how safe buildings and houses are in
India has gained prominence Engineers in seismic countries have the important
responsibility to ensure that the new construction is earthquake resistant and also they
must solve the problem posed by existing weak structures
It is expected that the handbook prepared by CAMTECH will be quite helpful to the
engineering personnel of Indian Railways engaged in construction and maintenance
activities of civil structures
CAMTECHGwalior (AR Tupe)
23 May 2017 Executive Director
भतमका
भारतीय रलव एक बड़ा सगठन ह जिसक पास ससववल इिीननयररग सरचनाओ एव भवनो की ववशाल सपदा मौिद ह भकप की ववनाशकारी परकनत को धयान म रखत हए यह आवशयक ह कक लगभग सभी भवनो चाह व आवासीय ससथागत शकषणिक इतयादद क हो उनकी योिना डििाइन ननमााि तथा रखरखाव भकप परनतरोधी तरीको को अपनाकर ककया िाना चादहए जिसस कक भकप क कारि मानव िीवन व सपवि क नकसान को नयनतम ककया िा सक
ldquoभकप परतिरोधी भवनो क तनरमाणrdquo पर यह हसतपजसतका एक िगह पर पयाापत सामगरी परदान करन का एक परयास ह ताकक वयजतत भवनो क भकप परनतरोधी ननमााि क सलए मलभत ससदधातो को ववकससत कर सही तथा वयवहाररक कायाववधध को अमल म ला सक
इस हसतपजसतका की सामगरी को गयारह अधयायो म ववभाजित ककया गया ह अधयमय-1 पररचय तथा अधयमय-2 भकप इिीननयररग म परयतत शबदावली पररभावित करता ह अधयमय-3 भकप व भकपी खतरो क बार म बननयादी जञान को सकषप म वणिात करता ह अधयमय- 4 भकप पररमाि तथा तीवरता क माप क साथ भारत क भकपीय ज़ोन मानधचतर भकप की ननगरानी क सलए एिससयो क बार म िानकारी परदान करता ह अधयमय-5 व 6 भवन लआउट म भकप परनतरोध क सधार क सलए वयापक ससदधात को बताता ह अधयमय-7 भवन की गनतशील परनतकिया को दशााता ह अधयमय-8 और 9 म कोि पर आधाररत पाशवा बल ननधाारि का तरीका तथा बहमजिला भवन की ldquoितटाइल डिटसलग तथा कपससटी डििाइनrdquo को धयान म रखत हए डििाइन का उदाहरि परसतत ककया गया ह अधयमय-10 म कम शजतत की धचनाई दवारा सरचनाओ क ननमााि को भकप परनतरोधी ससदधातो को धयान म रख वणिात ककया गया ह अधयमय -11 म मौिदा भवनो की भकप परनतरोधी आवशयकताओ को परा करन क सलए भवनो क मौिदा भकपरोधी मलयाकन और पनः सयोिन पर परकाश िाला गया ह
यह हसतपजसतका मखयतः भारतीय रल क फीलि तथा डििाइन कायाालय म कायारत िईएसएसई सतर क सलए ह इस हसतपजसतका को भारतीय रल क ससववल इिीननयसा तथा अनय ववभागो क इिीननयसा दवारा एक सदभा पजसतका क रप म भी इसतमाल ककया िा सकता ह
म शरी एस क ठतकर परोफसर (ररटायिा) आई आई टी रड़की को उनक दवारा ददय गए मागादशान तथा सझावो क सलए अतयनत आभारी ह तथा शरी क सी शातय एसएसईससववल को इस हसतपजसतका क सकलन म उनक समवपात सहयोग क सलए धनयवाद दता ह
यदयवप इस हसतपजसतका को तयार करन म हर तरह की सावधानी बरती गई ह कफर भी कोई तरदट या चक हो तो कपया IRCAMTECHGwalior की िानकारी म लायी िा सकती ह
भारतीय रल क सभी अधधकाररयो और इकाइयो दवारा पसतक की सामगरी म ववसतार तथा सधार क सलए ददय िान वाल सझावो का सवागत ह
कमटक गवातलयर (िी क गपता) 23 मई 2017 सोयकत तनदशकतसतवल
PREFACE
Indian Railways is a big organisation having large assets of Civil Engineering Structures
and Buildings Keeping in mind the destructive nature of Earthquake it is essential that
almost all buildings whether residential institutional educational assembly etc should
be planned designed constructed as well as maintained by adopting Earthquake
Resistant features so that loss due to earthquake to human lives and properties can be
minimised
This handbook on ldquoConstruction of Earthquake Resistant Buildingsrdquo is an attempt to
provide enough material at one place for individual to develop the basic concept for
correctly interpreting and using practices for earthquake resistant construction of
Buildings
Content of this handbook is divided into Eleven Chapters Chapter-1 is Introduction
and Chapter-2 defines Terminology frequently used in Earthquake Engineering
Chapter-3 describes in brief Basic knowledge about Earthquake amp Seismic Hazards
Chapter-4 deals with Measurement of Earthquake magnitude amp intensity with
information about Seismic Zoning Map of India and Agencies for Earthquake
monitoring Chapter-5 amp 6 elaborates General Principle for improving Earthquake
resistance in building layouts Chapter-7 features Dynamic Response of Building In
Chapter-8 amp 9 Codal based procedure for determining lateral loads and Design of
multi-storeyed building with solved example considering Ductile Detailing and Capacity
Design Concept is covered Chapter-10 describes Construction of Low strength
Masonry Structure considering earthquake resistant aspect Chapter-11 enlighten
ldquoSeismic Evaluation amp Retrofittingrdquo for structural upgrading of existing buildings to
meet the seismic requirements
This handbook is primarily written for JESSE level over Indian Railways working in
Field and Design office This handbook can also be used as a reference book by Civil
Engineers and Engineers of other departments of Indian Railways
I sincerely acknowledge the valuable guidance amp suggestion by Shri SK Thakkar
Professor (Retd) IIT Roorkee and also thankful to Shri KC Shakya SSECivil for his
dedicated cooperation in compilation of this handbook
Though every care has been taken in preparing this handbook any error or omission
may please be brought out to the notice of IRCAMTECHGwalior
Suggestion for addition and improvement in the contents from all officers amp units of
Indian Railways are most welcome
CAMTECHGwalior (DK Gupta)
23 May 2017 Joint DirectorCivil
तवषय-सची CONTENT
अधयाय CHAPTER
तववरण DESCRIPTION
पषठ
सोPAGE
NO
पराककथन FOREWORD FROM MEMBER ENGINEERING RLY BOARD पराककथन FOREWORD FROM ADG RDSO पराककथन FOREWORD FROM ED CAMTECH भतमका PREFACE
तवषय-सची CONTENT
सोशोधन पतचययाो CORRECTION SLIPS
1 पररचय Introduction 01
2 भको प इोजीतनयररोग क तलए शबदावली Terminology for Earthquake
Engineering 02-05
3 भको प क बार म About Earthquake 06-16
31 भको प Earthquake 06
32 नकि कारणसो स िसता ि भको प What causes Earthquake 06
33 नववतानिक गनतनवनि Tectonic Activity 06
34 नववतानिक पलट का नसदाोत Theory of Plate Tectonics 07
35 लचीला ररबाउोड नसदाोत Elastic Rebound Theory 11
36 भको प और दसष क परकार Types of Earthquakes and Faults 11
37 जमीि कस निलती ि How the Ground shakes 12
38 भको प या भको पी खतरसो का परभाव Effects of Earthquake or Seismic
Hazards 13
4 भको पी जोन और भको प का मापन Seismic Zone and Measurement
of Earthquake 17-28
41 भको पी जसि Seismic Zone 17
42 भको प का मापि Measurement of Earthquake 19
43 भको प पररमाण सकल क परकार Types of Earthquake Magnitude
Scales 20
44 भको प तीवरता Earthquake Intensity 22
45 भको प निगरािी और सवाओो क नलए एजनसयसो Agencies for Earthquake
Monitoring and Services 28
5 भवन म भको प परतिरोध म सधार क तलए सामानय तसदाोि General
Principle for improving Earthquake Resistance in Building 29-33
51 िलकापि Lightness 29
52 निमााण की निरोतरता Continuity of Construction 29
53 परसजसतटोग एवो ससपडड पाटटास Projecting and Suspended Parts 29
54 भवि की आकनत Shape of Building 29
55 सनविा जिक नबसतडोग लआउट Preferred Building Layouts 30
56 नवनभनन नदशाओो म शसति Strength in Various Directions 30
57 िी ोव Foundations 30
58 छत एवो मोनजल Roofs and Floors 30
59 सीनियाो Staircases 31
510 बॉकस परकार निमााण Box Type Construction 33
511 अनि सरिा Fire Safety 33
6
भको प क दौरान आर सी भवनो ो क परदशयन पर सटरकचरल अतनयतमििाओो
का परभाव Effect of Structural Irregularities on Performance of
RC Buildings during Earthquakes
34-38
61 सटर कचरल अनियनमतताओो का परभाव Effect of Structural Irregularities 34
62 िनतज अनियनमतताएो Horizontal Irregularities 34
63 ऊरधाािर अनियनमतताएो Vertical Irregularities 36
64
भवि नवनयास अनियनमतताएो ndash समसयाए ववशलिि एव ननदान क उपाय Building Irregularities ndash Problems Analysis and Remedial
Measures 37
7 भवन की िायनातमक तवशषिाएा Dynamic Characteristics of
Building 39-47
71 डायिानमक नवशषताए Dynamic Characteristics 39
72 पराकनतक अवनि Natural Period 39
73 पराकनतक आवनि Natural Frequency 39
74 पराकनतक अवनि कस परभानवत करि वाल कारक Factors influencing
Natural Period 40
75 Mode आकनत Mode Shape 42
76 Mode आकनतयसो कस परभानवत करि वाल कारक Factors influencing
Mode Shapes 44
77 सोरचिा की परनतनकरया Response of Structure 46
78 नडजाइि सपटर म Design Spectrum 46
8 तिजाइन पारशय बलो ो क तनधायरण क तलए कोि आधाररि िरीका Code
Based Procedure for Determination of Design Lateral Loads 48-59
81 भको पी नडजाइि की नफलससफ़ी Philosophy of Seismic Design 48
82 भको पी नवशलषण क नलए तरीक Methods for Seismic Analysis 48
83 डायिानमक नवशलषण Dynamic Analysis 49
84 पारशा बल परनकरया Lateral Force Procedure 49
85 को पि की मौनलक पराकनतक अवनि Fundamental Natural Period of
Vibration 52
86 नडजाइि पारशा बल Design Lateral Force 53
87 नडजाइि बल का नवतरण Distribution of Design Force 53
88 नडजाइि उदािरण Design Example ndash To determine Base Shear and
its distribution along Height of Building 54
9 ढााचागि सोरचना का तनमायण Construction of Framed Structure 60-90
91
गरतवाकषाण लसनडोग और भको प लसनडोग म आर सी नबसतडोग का वयविार Behaviour of RC Building in Gravity Loading and Earthquake
Loading 60
92 परबनलत को करीट इमारतसो पर िनतज भको प का परभाव Effect of Horizontal
Earthquake Force on RC Buildings 61
93 िमता नडजाइि सोकलपिा Capacity Design Concept 61
94 लचीलापि और ऊजाा का अपवयय Ductility and Energy Dissipation 62
95 lsquoमजबतिोभ ndash कमजसर बीमrsquo फलससफ़ी lsquoStrong Column ndash Weak
Beamrsquo Philosophy 62
96 कठसर डायाफराम नकरया Rigid Diaphragm Action 63
97
सॉफट सटसरी नबसतडोग क साथ ndash ओपि गराउोड सटसरी नबसतडोग जस नक भको प क
समय कमजसर िसती ि Building with Soft storey ndash Open Ground
Storey Building that is vulnerable in Earthquake 63
98 भको प क दौराि लघ कॉलम वाली इमारतसो का वयविार Behavior of
Buildings with Short Columns during Earthquakes 65
99 भको प परनतरसिी इमारतसो की लचीलापि आवशयकताए Ductility
requirements of Earthquake Resistant Buildings 66
910
बीम नजनह आर सी इमारतसो म भको प बलसो का नवरसि करि क नलए डाला जाता
ि Beams that are required to resist Earthquake Forces in RC
Buildings 66
911 फलकसचरल ममबसा क नलए सामानय आवशयकताए General Requirements
for Flexural Members 68
912
कॉलम नजनह आर सी इमारतसो म भको प बलसो का नवरसि करि क नलए डाला
जाता ि Columns that are required to resist Earthquake Forces in
RC Buildings 69
913 एकसीयल लसडड मबसा क नलए सामानय आवशयकताए General
Requirements for Axial Loaded Members 71
914 बीम-कॉलम जसड जस आर सी भविसो म भको प बलसो का नवरसि करत ि Beam-
Column Joints that resist Earthquakes Forces in RC Buildings 72
915 नवशष सीनमत सदढीकरण Special Confining Reinforcement 74
916
नवशषतः भको पीय ितर म कतरिी दीवारसो वाली इमारतसो का निमााण Construction of Buildings with Shear Walls preferably in Seismic
Regions 75
917 इमपरवड नडजाइि रणिीनतयाो Improved design strategies 76
918 नडजाइि उदािरण Design Example ndash Beam Design of RC Frame
with Ductile Detailing 78
10 अलप सामरथय तचनाई सोरचनाओो क तनमायण Construction of Low
Strength Masonry Structures 91-106
101 भको प क दौराि ईोट नचिाई की दीवारसो का वयविार Behaviour of
Brick Masonry Walls during Earthquakes 91
102 नचिाई वाली इमारतसो म बॉकस एकशि कस सनिनित कर How to ensure
Box Action in Masonry Buildings 92
103 िनतज बड की भनमका Role of Horizontal Bands 93
104 अिसलोब सदढीकरण Vertical Reinforcement 95
105 दीवारसो म सराखसो का सोरिण Protection of Openings in Walls 96
106
भको प परनतरसिी ईोट नचिाई भवि क निमााण ित सामानय नसदाोत General
Principles for Construction of Earthquake Resistant Brick
Masonry Building
97
107 ओपनिोग का परभाव Influence of Openings 100
108 िारक दीवारसो म ओपनिोग परदाि करि की सामानय आवशयकताए General Requirements of Providing Openings in Bearing Walls
100
109 भको पी सदिीकरण वयवसथा Seismic Strengthening Arrangements 101
1010 भको प क दौराि सटसि नचिाई की दीवारसो का वयविार Behaviour of Stone
Masonry Walls during Earthquakes 104
1011
भकप परनतरोधी सटोन धचनाई क ननमााि हत सामानय ससदधात General
Principles for Construction of Earthquake Resistant Stone
Masonry Building
104
11 भकपीय रलयमकन और रटरोफिट ग Seismic Evaluation and
Retrofitting 107-142
111 भकपीय मलयाकन Seismic Evaluation 107
112 भवनो की रटरोकिदटग Retrofitting of Building 116
113
आरसी भवनो क घटको म सामानय भकपी कषनतया और उनक उपचार Common seismic damage in components of RC
Buildings and their remedies 133
114 धचनाई सरचनाओ की रटरोकिदटग Retrofitting of Masonry
Structures 141
Annex ndash I भारिीय भको पी सोतििाएा Indian Seismic Codes 143-145
Annex ndash II Checklist Multiple Choice Questions for Points to be kept in
mind during Construction of Earthquake Resistant Building 146-151
सोदभयगरोथ सची BIBLIOGRAPHY 152
तटपपणी NOTES 153-154
हमारा उददशय एव डिसकलरर OUR OBJECTIVE AND DISCLAIMER
सोशसिि पनचायसो का परकाशि
ISSUE OF CORRECTION SLIPS
इस ििपसतिका क नलए भनवषय म परकानशत िसि वाली सोशसिि पनचायसो कस निमनािसार सोखाोनकत
नकया जाएगा
The correction slips to be issued in future for this handbook will be numbered as
follows
कमटक2017नसईआरबी10सीएस XX नदिाोक_____________________
CAMTECH2017CERB10CS XX date_________________________
जिा xx सोबसतित सोशसिि पची की करम सोखा ि (01 स परारमभ िसकर आग की ओर)
Where ldquoXXrdquo is the serial number of the concerned correction slip (starting
from 01 onwards)
परकातशि सोशोधन पतचययाा W a
CORRECTION SLIPS ISSUED
करसो Sr No
परकाशन
तदनाोक Date of
issue
सोशोतधि पषठ सोखया िथा मद सोखया Page no and Item No modified
तटपपणी Remarks
कमटक2017नसईआरबी10
CAMTECH2017CERB10
भकमप परनतरसिी भवि निमााण मई ndash 2017 CONSTRUCTION OF EARTHQUAKE RESISTANT BUILDING May ndash 2017
1
अधयाय Chapter ndash 1
पररचय Introduction
To avoid a great earthquake disaster with its severe consequences special consideration must be
given Engineers in seismic countries have the important responsibility to ensure that the new
construction is earthquake resistant and also they must solve the problem posed by existing weak
structures
Most of the loss of life in past earthquakes has occurred due to the collapse of buildings
constructed with traditional materials like stone brick adobe (kachcha house) and wood which
were not particularly engineered to be earthquake resistant In view of the continued use of such
buildings it is essential to introduce earthquake resistance features in their construction
The problem of earthquake engineering can be divided into two parts first to design new
structures to perform satisfactorily during an earthquake and second to retrofit existing structures
so as to reduce the loss of life during an earthquake Every city in the world has a significant
proportion of existing unsafe buildings which will produce a disaster in the event of a strong
ground shaking Engineers have the responsibility to develop appropriate methods of retrofit
which can be applied when the occasion arises
The design of new building to withstand ground shaking is prime responsibility of engineers and
much progress has been made during the past 40 years Many advances have been made such as
the design of ductile reinforced concrete members Methods of base isolation and methods of
increasing the damping in structures are now being utilized for important buildings both new and
existing Improvements in seismic design are continuing to be made such as permitting safe
inelastic deformations in the event of very strong ground shaking
A problem that the engineer must share with the seismologistgeologist is that of prediction of
future occurrence of earthquake which is not possible in current scenario
Earthquake resistant construction requires seismic considerations at all stages from architectural
planning to structural design to actual constructions and quality control
Problems pertaining to Earthquake engineering in a seismic country cannot be solved in a short
time so engineers must be prepared to continue working to improve public safety during
earthquake In time they must control the performance of structures so that effect of earthquake
does not create panic in society and its after effects are easily restorable
To ensure seismic resistant construction earthquake engineering knowledge needs to spread to a
broad spectrum of professional engineers within the country rather than confining it to a few
organizations or individuals as if it were a super-speciality
कमटक2017नसईआरबी10
CAMTECH2017CERB10
भकमप परनतरसिी भवि निमााण मई ndash 2017 CONSTRUCTION OF EARTHQUAKE RESISTANT BUILDING May ndash 2017
2
अधयाय Chapter ndash 2
भको प इोजीतनयररोग क तलए शबदावली Terminology for Earthquake Engineering
21 फोकस या िाइपोसटर Focus or Hypocenter
In an earthquake the waves emanate from a finite area
of rocks However the point from which the waves
first emanate or where the fault movement starts is
called the earthquake focus or hypocenter
22 इपीसटर Epicentre
The point on the ground surface just above the focus is called the epicentre
23 सििी फोकस भको प Shallow Focus Earthquake
Shallow focus earthquake occurs where the focus is less than 70 km deep from ground surface
24 इोटरमीतिएट फोकस भको प Intermediate Focus Earthquake
Intermediate focus earthquake occurs where the focus is between 70 km to 300 km deep
25 गिरा फोकस भको प Deep Focus Earthquake
Deep focus earthquake occurs where the depth of focus is more than 300 km
26 इपीसटर दरी Epicentre Distance
Distance between epicentre and recording station in km or in degrees is called epicentre distance
27 पवय क झटक Foreshocks
Fore shocks are smaller earthquakes that precede the main earthquake
28 बाद क झटक Aftershocks
Aftershocks are smaller earthquakes that follow the main earthquake
29 पररमाण Magnitude
The magnitude of earthquake is a number which is a measure of energy released in an
earthquake It is defined as logarithm to the base 10 of the maximum trace amplitude expressed
in microns which the standard short-period torsion seismometer (with a period of 08s
Fig 21Basic terminology
कमटक2017नसईआरबी10
CAMTECH2017CERB10
भकमप परनतरसिी भवि निमााण मई ndash 2017 CONSTRUCTION OF EARTHQUAKE RESISTANT BUILDING May ndash 2017
3
magnification 2800 and damping nearly critical) would register due to the earthquake at an
epicentral distance of 100 km
210 िीवरिा Intensity
The intensity of an earthquake at a place is a measure of the strength of shaking during the
earthquake and is indicated by a number according to the modified Mercalli Scale or MSK
Scale of seismic intensities
211 पररमाण और िीवरिा क बीच बतनयादी फकय Basic difference between Magnitude and
Intensity
Magnitude of an earthquake is a measure of its size
whereas intensity is an indicator of the severity of
shaking generated at a given location Clearly the
severity of shaking is much higher near the
epicenter than farther away
This can be elaborated by considering the analogy
of an electric bulb Here the size of the bulb (100-
Watt) is like the magnitude of an earthquake (M)
and the illumination (measured in lumens) at a
location like the intensity of shaking at that location
(Fig 22)
212 दरवण Liquefaction
Liquefaction is a state in saturated cohesion-less soil wherein the effective shear strength is
reduced to negligible value for all engineering purpose due to pore pressure caused by vibrations
during an earthquake when they approach the total confining pressure In this condition the soil
tends to behave like a fluid mass
213 तववियतनक लकषण Tectonic Feature
The nature of geological formation of the bedrock in the earthrsquos crust revealing regions
characterized by structural features such as dislocation distortion faults folding thrusts
volcanoes with their age of formation which are directly involved in the earth movement or
quake resulting in the above consequences
214 भको पी दरवयमान Seismic Mass
It is the seismic weight divided by acceleration due to gravity
215 भको पी भार Seismic Weight
It is the total dead load plus appropriate amounts of specified imposed load
Fig 22 Reducing illumination with distance
from an electric bulb
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216 आधार Base
It is the level at which inertia forces generated in the structure are transferred to the foundation
which then transfers these forces to the ground
217 दरवयमान का क दर Centre of Mass
The point through which the resultant of the masses of a system acts is called Centre of Mass
This point corresponds to the centre of gravity of masses of system
218 कठोरिा का क दर Centre of Stiffness
The point through which the resultant of the restoring forces of a system acts is called Centre of
stiffness
219 बॉकस परणाली Box System
Box is a bearing wall structure without a space frame where the horizontal forces are resisted by
the walls acting as shear walls
220 पटटा Band
A reinforced concrete reinforced brick or wooden runner provided horizontally in the walls to tie
them together and to impart horizontal bending strength in them
221 लचीलापन Ductility
Ductility of a structure or its members is the capacity to undergo large inelastic deformations
without significant loss of strength or stiffness
222 किरनी दीवार Shear Wall
Shear wall is a wall that is primarily designed to resist lateral forces in its own plane
223 िनय का बयौरा Ductile Detailing
Ductile Detailing is the preferred choice of location and amount of reinforcement in reinforced
concrete structures to provide adequate ductility In steel structures it is the design of members
and their connections to make them adequate ductile
224 लचीला भको पी तवरण गणाोक Elastic Seismic Acceleration Co-Efficient A
This is the horizontal acceleration value as a fraction of acceleration due to gravity versus
natural period of vibration T that shall be used in design of structures
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225 पराकतिक अवतध Natural Period T
Natural period of a structure is its time period of undamped vibration
a) Fundamental Natural Period Tl It is the highest modal time period of vibration along the
considered direction of earthquake motion
b) Modal Natural Period Tk Modal natural period of mode k is the time period of vibration in
mode k
226 नॉमयल मोि Normal Mode
Mode of vibration at which all the masses in a structure attain maximum values of displacements
and rotations and also pass through equilibrium positions simultaneously
227 ओवरसटरगथ Overstrength
Strength considering all factors that may cause its increase eg steel strength being higher than
the specified characteristic strength effect of strain hardening in steel with large strains and
concrete strength being higher than specified characteristic value
228 ररसाोस कमी कारक Response Reduction Factor R
The factor by which the actual lateral force that would be generated if the structure were to
remain elastic during the most severe shaking that is likely at that site shall be reduced to obtain
the design lateral force
229 ररसाोस सकटर म Response Spectrum
The representation of the maximum response of idealized single degree freedom system having
certain period and damping during that earthquake The maximum response is plotted against the
undamped natural period and for various damping values and can be expressed in terms of
maximum absolute acceleration maximum relative velocity or maximum relative displacement
230 तमटटी परोफ़ाइल फकटर Soil Profile Factor S
A factor used to obtain the elastic acceleration spectrum depending on the soil profile below the
foundation of structure
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अधयाय Chapter ndash 3
भको प क बार म About Earthquake
31 भको प Earthquake
Vibrations of earthrsquos surface caused by waves coming from a source of disturbance inside the
earth are described as earthquakes
Earthquake is a natural phenomenon occurring with all uncertainties
During the earthquake ground motions occur in a random fashion both horizontally and
vertically in all directions radiating from epicentre
These cause structures to vibrate and induce inertia forces on them
32 तकन कारणो ो स िोिा ि भको प What causes Earthquake
Earthquakes may be caused by
Tectonic activity
Volcanic activity
Land-slides and rock-falls
Rock bursting in a mine
Nuclear explosions
33 तववियतनक गतितवतध Tectonic Activity
Tectonic activity pertains to geological formation of the bedrock in the earthrsquos crust characterized
by structural features such as dislocation distortion faults folding thrusts volcanoes directly
involved in the earth movement
As engineers we are interested in earthquakes that are large enough and close enough (to the
structure) to cause concern for structural safety- usually caused by tectonic activity
Earth (Fig 31) consists of following segments ndash
solid inner core (radius ~1290km) that consists of heavy
metals (eg nickel and iron)
liquid outer core(thickness ~2200km)
stiffer mantle(thickness ~2900km) that has ability to flow
and
crust(thickness ~5 to 40km) that consists of light
materials (eg basalts and granites)
At the Core the temperature is estimated to be ~2500degC the
pressure ~4 million atmospheres and density ~135 gmcc
this is in contrast to ~25degC 1 atmosphere and 15 gmcc on the surface of the Earth
Fig 31 Inside the Earth
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Due to prevailing high temperature and pressure gradients between the Crust and the Core the
local convective currents in mantle (Fig 32) are developed These convection currents result in a
circulation of the earthrsquos mass hot molten lava comes out and the cold rock mass goes into the
Earth The mass absorbed eventually melts under high temperature and pressure and becomes a
part of the Mantle only to come out again from another location
Near the bottom of the crust horizontal component currents impose shear stresses on bottom of
crust causing movement of plates on earthrsquos surface The movement causes the plates to move
apart in some places and to converge in others
34 तववियतनक पलट का तसदाोि Theory of Plate Tectonics
Tectonic Plates Basic hypothesis of plate tectonics is that the earthrsquos surface consists of a
number of large intact blocks called plates or tectonic plates and these plates move with respect
to each other due to the convective flows of Mantle material which causes the Crust and some
portion of the Mantle to slide on the hot molten outer core The major plates are shown in
Fig 33
The earthrsquos crust is divided into six continental-sized plates (African American Antarctic
Australia-Indian Eurasian and Pacific) and about 14 of sub-continental size (eg Carribean
Cocos Nazca Philippine etc) Smaller platelets or micro-plates also have broken off from the
larger plates in the vicinity of many of the major plate boundaries
Fig 32 Convention current in mantle
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Fig 33 The major tectonic plates mid-oceanic ridges trenches and transform faults of
the earth Arrows indicate the directions of plate movement
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The relative deformation between plates occurs only in narrow zones near their boundaries
These deformations are
1 Aseismic deformation This deformation of the plates occurs slowly and continuously
2 Seismic deformation This deformation occurs with sudden outburst of energy in the form of
earthquakes
The boundaries are (i) Convergent (ii) Divergent (iii) Transform
Convergent boundary Sometimes the plate in the front is slower Then the plate behind it
comes and collides (and mountains are formed) This type of inter-plate interaction is the
convergent boundary (Fig 34)
Divergent boundary Sometimes two plates move away from one another (and rifts are
created) This type of inter-plate interaction is the divergent boundary (Fig 35)
Transform boundary Sometimes two plates move side-by-side along the same direction or in
opposite directions This type of inter-plate interaction is the transform boundary (Fig 36)
Since the deformation occurs predominantly at the boundaries between the plates it would be
expected that the locations of earthquakes would be concentrated near plate boundaries The map
of earthquake epicentres shown in Fig 37 provides strong support to confirm the theory of plate
tectonics The dots represent the epicentres of significant earthquakes It is apparent that the
locations of the great majority of earthquakes correspond to the boundaries between plates
Fig 34 Convergent Boundary
Fig 35 Divergent Boundary
Fig 36 Transform Boundary
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Fig 37 Worldwide seismic activity
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35 लचीला ररबाउोि तसदाोि Elastic Rebound Theory
Earth crust for some reason is moving in opposite
directions on certain faults This sets up elastic
strains in the rocks in the region near this fault As
the motion goes on the stresses build up in the
rocks until the stresses are large enough to cause
slip between the two adjoining portions of rocks
on either side A rupture takes place and the
strained rock rebounds back due to internal stress
Thus the strain energy in the rock is relieved
partly or fully (Fig 38)
Fault The interface between the plates where the movement has taken place is called fault
Slip When the rocky material along the interface of the plates in the Earthrsquos Crust reaches its
strength it fractures and a sudden movement called slip takes place
The sudden slip at the fault causes the earthquake A violent shaking of the Earth during
which large elastic strain energy released spreads out in the form of seismic waves that travel
through the body and along the surface of the
Earth
After elastic rebound there is a readjustment and
reapportion of the remaining strains in the region
The stress grows on a section of fault until slip
occurs again this causes yet another even though
smaller earthquake which is termed as aftershock
The aftershock activity continues until the
stresses are below the threshold level everywhere
in the rock
After the earthquake is over the process of strain build-up at this modified interface between the
tectonic plates starts all over again This is known as the Elastic Rebound Theory (Fig 39)
36 भको प और दोष क परकार Types of Earthquakes and Faults
Inter-plate Earthquakes Most earthquakes occurring along the boundaries of the tectonic
plates are called Inter-plate Earthquakes (eg 1897
Assam (India) earthquake)
Intra-plate Earthquakes Numbers of earthquakes
occurring within the plate itself but away from the
plate boundaries are called Intra-plate Earthquakes
(eg 1993 Latur (India) earthquake)
Note In both types of earthquakes the slip
generated at the fault during earthquakes is along
Fig 310 Type of Faults
Fig 38 Elastic Strain Build-Up and Brittle Rupture
Fig 39 Elastic Rebound Theory
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both vertical and horizontal directions (called Dip Slip) and lateral directions (called Strike
Slip) with one of them dominating sometimes (Fig 310)
37 जमीन कस तिलिी ि How the Ground shakes
Seismic waves Large strain energy released during an earthquake travels as seismic waves in all
directions through the Earthrsquos layers reflecting and refracting at each interface (Fig 311)
There are of two types of waves 1) Body Waves
2) Surface Waves
Body waves are of two types
a) Primary Waves (P-Wave)
b) Secondary Wave (S-Wave)
Surface waves are of two types namely
a) Love Waves
b) Rayleigh Waves
Body Waves Body waves have spherical wave front They consist of
Primary Waves (P-waves) Under P-waves [Fig 311(a)] material particles undergo
extensional and compressional strains along direction of energy transmission These waves
are faster than all other types of waves
Secondary Waves (S-waves) Under S-waves [Fig 311(b)] material particles oscillate at
Fig 311 Arrival of Seismic Waves at a Site
Fig 311(a) Motions caused by Primary Waves
Fig 311(b) Motions caused by Secondary Waves
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right angles to direction of energy transmission This type of wave shears the rock particle to
the direction of wave travel Since the liquid has no shearing resistance these waves cannot
pass through liquids
Surface Waves Surface waves have cylindrical wave front They consist of
Love Waves In case of Love waves [Fig 311(c)] the displacement is transverse with no
vertical or longitudinal components (ie similar to secondary waves with no vertical
component) Particle motion is restricted to near the surface Love waves being transverse
waves these cannot travel in liquids
Rayleigh Waves Rayleigh waves [Fig 311(d)] make a material particle oscillate in an
elliptic path in the vertical plane with horizontal motion along direction of energy
transmission
Note Primary waves are fastest followed in sequence by Secondary Love and Rayleigh waves
38 भको प या भको पी खिरो ो का परभाव Effects of Earthquake or Seismic Hazards
Basic causes of earthquake-induced damage are
Ground shaking
Structural hazards
Liquefaction
Ground failure Landslides
Tsunamis and
Fire
Fig 311(c) Motions caused by Love Waves
Fig 311(d) Motions caused by Rayleigh Waves
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381 जमीन को पन Ground shaking
Ground shaking can be considered to be the most important of all seismic hazards because all
the other hazards are caused by ground shaking
When an earthquake occurs seismic waves radiate away from the source and travel rapidly
through the earthrsquos crust
When these waves reach the ground surface they produce shaking that may last from seconds
to minutes
The strength and duration of shaking at a particular site depends on the size and location of
the earthquake and on the characteristics of the site
At sites near the source of a large earthquake ground shaking can cause tremendous damage
Where ground shaking levels are low the other seismic hazards may be low or nonexistent
Strong ground shaking can produce extensive damage from a variety of seismic hazards
depending upon the characteristics of the soil
The characteristics of the soil can greatly influence the nature of shaking at the ground
surface
Soil deposits tend to act as ldquofiltersrdquo to seismic waves by attenuating motion at certain
frequencies and amplifying it at others
Since soil conditions often vary dramatically over short distances levels of ground shaking
can vary significantly within a small area
One of the most important aspects of geotechnical earthquake engineering practice involves
evaluation of the effects of local soil conditions on strong ground motion
382 सोरचनातमक खिर Structural Hazards
Without doubt the most dramatic and memorable images of earthquake damage are those of
structural collapse which is the leading cause of death and economic loss in many
earthquakes
As the earth vibrates all buildings on the ground surface will respond to that vibration in
varying degrees
Earthquake induced accelerations velocities and displacements can damage or destroy a
building unless it has been designed and constructed or strengthened to be earthquake
resistant
The effect of ground shaking on buildings is a principal area of consideration in the design of
earthquake resistant buildings
Seismic design loads are extremely difficult to determine due to the random nature of
earthquake motions
Structures need not collapse to cause death and damage Falling objects such as brick facings
and parapets on the outside of a structure or heavy pictures and shelves within a structure
have caused casualties in many earthquakes Interior facilities such as piping lighting and
storage systems can also be damaged during earthquakes
However experiences from past strong earthquakes have shown that reasonable and prudent
practices can keep a building safe during an earthquake
Over the years considerable advancement in earthquake-resistant design has moved from an
emphasis on structural strength to emphases on both strength and ductility In current design
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practice the geotechnical earthquake engineer is often consulted for providing the structural
engineer with appropriate design ground motions
383 दरवीकरण Liquefaction
In some cases earthquake damage have occurred when soil deposits have lost their strength and
appeared to flow as fluids This phenomenon is termed as liquefaction In liquefaction the
strength of the soil is reduced often drastically to the point where it is unable to support
structures or remain stable Because it only occurs in saturated soils liquefaction is most
commonly observed near rives bays and other bodies of water
Soil liquefaction can occur in low density saturated sands of relatively uniform size The
phenomenon of liquefaction is particularly important for dams bridges underground pipelines
and buildings standing on such ground
384 जमीन तवफलिा लि सलाइि Ground Failure Land slides
1) Earthquake-induced ground Failure has been observed in the form of ground rupture along
the fault zone landslides settlement and soil liquefaction
2) Ground rupture along a fault zone may be very limited or may extend over hundreds of
kilometers
3) Ground displacement along the fault may be horizontal vertical or both and can be
measured in centimetres or even metres
4) A building directly astride such a rupture will be severely damaged or collapsed
5) Strong earthquakes often cause landslides
6) In a number of unfortunate cases earthquake-induced landslides have buried entire towns
and villages
7) Earthquake-induced landslides cause damage by destroying buildings or disrupting bridges
and other constructed facilities
8) Many earthquake-induced landslides result from liquefaction phenomenon
9) Others landslides simply represent the failures of slopes that were marginally stable under
static conditions
10) Landslide can destroy a building the settlement may only damage the building
385 सनामी Tsunamis
1) Tsunamis or seismic sea waves are generally produced by a sudden movement of the ocean
floor
2) Rapid vertical seafloor movements caused by fault rupture during earthquakes can produce
long-period sea waves ie Tsunamis
3) In the open sea tsunamis travel great distances at high speeds but are difficult to detect ndash
they usually have heights of less than 1 m and wavelengths (the distance between crests) of
several hundred kilometres
4) As a tsunami approaches shore the decreasing water depth causes its speed to decrease and
the height of the wave to increase
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5) As the water waves approach land their velocity decreases and their height increases from
5 to 8 m or even more
6) In some coastal areas the shape of the seafloor may amplify the wave producing a nearly
vertical wall of water that rushes far inland and causes devastating damage
7) Tsunamis can be devastating for buildings built in coastal areas
386 अति Fire
When the fire following an earthquake starts it becomes difficult to extinguish it since a strong
earthquake is accompanied by the loss of water supply and traffic jams Therefore the
earthquake damage increases with the earthquake-induced fire in addition to the damage to
buildings directly due to earthquakes
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अधयाय Chapter ndash 4
भको पी जोन और भको प का मापन Seismic Zone and Measurement of Earthquake
41 भको पी जोन Seismic Zone
Due to convective flow of mantle material crust of Earth and some portion of mantle slide on hot
molten outer core This sliding of Earthrsquos mass takes place in pieces called Tectonic Plates The
surface of the Earth consists of seven major tectonic plates (Fig 41)
They are
1 Eurasian Plate
2 Indo-Australian Plate
3 Pacific Plate
4 North American Plate
5 South American Plate
6 African Plate
7 Antarctic Plate
India lies at the northwestern end of the Indo Australian Plate (Fig 42) This Plate is colliding
against the huge Eurasian Plate and going under the Eurasian Plate Three chief tectonic sub-
regions of India are
the mighty Himalayas along the north
the plains of the Ganges and other rivers and
the peninsula
Most earthquakes occur along the Himalayan plate boundary (these are inter-plate earthquakes)
but a number of earthquakes have also occurred in the peninsular region (these are intra-plate
earthquakes)
Fig 41 Major Tectonic Plates on the Earthrsquos surface
Fig 42 Geographical Layout and Tectonic Plate
Boundaries in India
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Bureau of Indian Standards [IS1893 (part ndash 1) 2002] based on various scientific inputs from a
number of agencies including earthquake data supplied by Indian Meteorological Department
(IMD) has grouped the country into four seismic zones viz Zone II III IV and V Of these
Zone V is rated as the most seismically prone region while Zone II is the least (Fig 43)
Indian Seismic code (IS 18932002) divides the country into four seismic zones based on the
expected intensity of shaking in future earthquake The four zones correspond to areas that have
potential for shaking intensity on MSK scale as shown in the table
Seismic Zone Intensity on MSK scale of total area
II (Low intensity zone) VI (or less) 43
III (Moderate intensity zone) VII 27
IV (Severe intensity zone) VIII 18
V (Very Severe intensity zone) IX (and above) 12
Fig 43 Map showing Seismic Zones of India [IS 1893 (Part 1) 2002]
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42 भको प का मापन Measurement of Earthquake
421 मापन उपकरण Measuring Instruments
Seismograph The instrument that measures earthquake shaking is known as a seismograph
(Fig 44) It has three components ndash
Sensor ndash It consists of pendulum mass
string magnet and support
Recorder ndash It consists of drum pen and
chart paper
Timer ndash It consists of the motor that rotates
the drum at constant speed
Seismoscopes Some instruments that do not
have a timer device provide only the maximum
extent (or scope) of motion during the
earthquake
Digital instruments The digital instruments using modern computer technology records the
ground motion on the memory of the microprocessor that is in-built in the instrument
Note The analogue instruments have evolved over time but today digital instruments are more
commonly used
422 मापन क सकल Scale of Measurement
The Richter Magnitude Scale (also called Richter scale) assigns a magnitude number to quantify
the energy released by an earthquake Richter scale is a base 10 logarithmic scale which defines
magnitude as the logarithm of the ratio of the amplitude of the seismic wave to an arbitrary minor
amplitude
The magnitude M of an Earthquake is defined as
M = log10 A - log10 A0
Where
A = Recorded trace amplitude for that earthquake at a given distance as written by a
standard type of instrument (say Wood Anderson instrument)
A0 = Same as A but for a particular earthquake selected as standard
This number M is thus independent of distance between the epicentre and the station and is a
characteristic of the earthquake The standard shock has been defined such that it is low enough
to make the magnitude of most of the recorded earthquakes positive and is assigned a magnitude
of zero Thus if A = A0
Fig 44 Schematic of Early Seismograph
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M = log10 A0 - log10 A0 = 0
Standard shock of magnitude zero It is defined as one that records peak amplitude of one
thousandths of a millimetre at a distance of 100 km from the epicentre
1) Zero magnitude does not mean that there is no earthquake
2) Magnitude of an earthquake can be a negative number also
3) An earthquake that records peak amplitude of 1 mm on a standard seismograph at 100 km
will have its magnitude as
M = log10 (1) - log10 (10-3
)= 0 ndash (-3) = 3
Magnitude of a local earthquake It is defined as the logarithm to base 10 of the maximum
seismic wave amplitude (in thousandths of a mm) recorded on Wood Anderson seismograph at a
distance of 100 kms from the earthquake epicentre
1) With increase in magnitude by 10 the energy released by an earthquake increases by a
factor of about 316
2) A magnitude 80 earthquake releases about 316 times the energy released by a magnitude
70 earthquake or about 1000 times the energy released by a 60 earthquake
3) With increase in magnitude by 02 the energy released by the earthquake doubles
43 भको प पररमाण सकल क परकार Types of Earthquake Magnitude Scales
Several scales have historically been described as the ldquoRitcher Scalerdquo The Ritcher local
magnitude (ML) is the best known magnitude scale but it is not always the most appropriate scale
for description of earthquake size The Ritcher local magnitude does not distinguish between
different types of waves
At large epicentral distances body waves have usually been attenuated and scattered sufficiently
that the resulting motion is dominated by surface waves
Other magnitude scales that base the magnitude on the amplitude of a particular wave have been
developed They are
a) Surface Wave Magnitude (MS)
b) Body Wave Magnitude (Mb)
c) Moment Magnitude (Mw)
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431 सिि लिर पररमाण Surface Wave Magnitude (MS)
The surface wave magnitude (Gutenberg and Ritcher 1936) is a worldwide magnitude scale
based on the amplitude of Rayleigh waves with period of about 20 sec The surface wave
magnitude is obtained from
MS = log A + 166 log Δ + 20
Where A is the maximum ground displacement in micrometers and Δ is the epicentral distance of
the seismometer measured in degrees (3600 corresponding to the circumference of the earth)
The surface wave magnitude is most commonly used to describe the size of shallow (less than
about 70 km focal depth) distant (farther than about 1000 km) moderate to large earthquakes
432 बॉिी लिर पररमाण Body Wave Magnitude (Mb)
For deep-focus earthquakes surface waves are often too small to permit reliable evaluation of the
surface wave magnitude The body wave magnitude (Gutenberg 1945) is a worldwide magnitude
scale based on the amplitude of the first few cycles of p-waves which are not strongly influenced
by the focal depth (Bolt 1989) The body wave magnitude can be expressed as
Mb = log A ndash log T + 001Δ + 59
Where A is the p-wave amplitude in micrometers and T is the period of the p-wave (usually
about one sec)
Saturation
For strong earthquakes the measured
ground-shaking characteristics become
less sensitive to the size of the
earthquake than the smaller earthquakes
This phenomenon is referred to as
saturation (Fig 45)
The body wave and the Ritcher local
magnitudes saturate at magnitudes of 6
to 7 and the surface wave magnitude
saturates at about Ms = 8
To describe the size of a very large
earthquake a magnitude scale that does
not depend on ground-shaking levels
and consequently does not saturate
would be desirable
Fig 45 Saturation of various magnitude scale Mw (Moment
Magnitude) ML (Ritcher Local Magnitude) MS (Surface Wave
Magnitude) mb (Short-period Body Wave Magnitude) mB
(Long-period Body Wave Magnitude) and MJMA (Japanese
Meteorological Agency Magnitude)
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433 पल पररमाण Moment Magnitude (Mw)
The only magnitude scale that is not subject to saturation is the moment magnitude
The moment magnitude is given by
Mw = [(log M0)15] ndash 107
Where M0 is the seismic moment in dyne-cm
44 भको प िीवरिा Earthquake Intensity
Earthquake magnitude is simply a measure of the size of the earthquake reflecting the elastic
energy released by the earthquake It is usually referred by a certain real number on the Ritcher
scale (eg magnitude 65 earthquake)
On the other hand earthquake intensity indicates the extent of shaking experienced at a given
location due to a particular earthquake It is usually referred by a Roman numeral on the
Modified Mercalli Intensity (MMI) scale as given below
I Not felt except by a very few under especially favourable circumstances
II Felt by only a few persons at rest especially on upper floors of buildings delicately
suspended objects may swing
III Felt quite noticeably indoors especially on upper floors of buildings but many people
do not recognize it as an earthquake standing motor cars may rock slightly vibration
like passing of truck duration estimated
IV During the day felt indoors by many outdoors by few at night some awakened
dishes windows doors disturbed walls make cracking sound sensation like heavy
truck striking building standing motor cars rocked noticeably
V Felt by nearly everyone many awakened some dishes windows etc broken a few
instances of cracked plaster unstable objects overturned disturbances of trees piles
and other tall objects sometimes noticed pendulum clocks may stop
VI Felt by all many frightened and run outdoors some heavy furniture moved a few
instances of fallen plaster or damaged chimneys damage slight
VII Everybody runs outdoors damage negligible in buildings of good design and
construction slight to moderate in well-built ordinary structures considerable in
poorly built or badly designed structures some chimneys broken noticed by persons
driving motor cars
VIII Damage slight in specially designed structures considerable in ordinary substantial
buildings with partial collapse great in poorly built structures panel walls thrown out
of frame structures fall of chimneys factory stacks columns monuments walls
heavy furniture overturned sand and mud ejected in small amounts changes in well
water persons driving motor cars disturbed
IX Damage considerable in specially designed structures well-designed frame structures
thrown out of plumb great in substantial buildings with partial collapse buildings
shifted off foundations ground cracked conspicuously underground pipes broken
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X Some well-built wooden structures destroyed most masonry and frame structures
destroyed with foundations ground badly cracked rails bent landslides considerable
from river banks and steep slopes shifted sand and mud water splashed over banks
XI Few if any (masonry) structures remain standing bridges destroyed broad fissures in
ground underground pipelines completely out of service earth slumps and land slips
in soft ground rails bent greatly
XII Damage total practically all works of construction are damaged greatly or destroyed
waves seen on ground surface lines of sight and level are destroyed objects thrown
into air
441 MSK िीवरिा सकल MSK Intensity Scale
The MSK intensity scale is quite comparable to the Modified Mercalli intensity scale but is more
convenient for application in field and is widely used in India In assigning the MSK intensity
scale at a site due attention is paid to
Type of Structures (Table ndash A)
Percentage of damage to each type of structure (Table ndash B)
Grade of damage to different types of structures (Table ndash C)
Details of Intensity Scale (Table ndash D)
The main features of MSK intensity scale are as follows
Table ndash A Types of Structures (Buildings)
Type of
Structures
Definitions
A Building in field-stone rural structures unburnt ndash brick houses clay houses
B Ordinary brick buildings buildings of large block and prefabricated type half
timbered structures buildings in natural hewn stone
C Reinforced buildings well built wooden structures
Table ndash B Definition of Quantity
Quantity Percentage
Single few About 5 percent
Many About 50 percent
Most About 75 percent
Table ndash C Classification of Damage to Buildings
Grade Definitions Descriptions
G1 Slight damage Fine cracks in plaster fall of small pieces of plaster
G2 Moderate damage Small cracks in plaster fall of fairly large pieces of plaster
pantiles slip off cracks in chimneys parts of chimney fall down
G3 Heavy damage Large and deep cracks in plaster fall of chimneys
G4 Destruction Gaps in walls parts of buildings may collapse separate parts of
the buildings lose their cohesion and inner walls collapse
G5 Total damage Total collapse of the buildings
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Table ndash D Details of Intensity Scale
Intensity Descriptions
I Not noticeable The intensity of the vibration is below the limits of sensibility
the tremor is detected and recorded by seismograph only
II Scarcely noticeable
(very slight)
Vibration is felt only by individual people at rest in houses
especially on upper floors of buildings
III Weak partially
observed only
The earthquake is felt indoors by a few people outdoors only in
favourable circumstances The vibration is like that due to the
passing of a light truck Attentive observers notice a slight
swinging of hanging objects somewhat more heavily on upper
floors
IV Largely observed The earthquake is felt indoors by many people outdoors by few
Here and there people awake but no one is frightened The
vibration is like that due to the passing of a heavily loaded truck
Windows doors and dishes rattle Floors and walls crack
Furniture begins to shake Hanging objects swing slightly Liquid
in open vessels are slightly disturbed In standing motor cars the
shock is noticeable
V Awakening
a) The earthquake is felt indoors by all outdoors by many Many
people awake A few run outdoors Animals become uneasy
Buildings tremble throughout Hanging objects swing
considerably Pictures knock against walls or swing out of
place Occasionally pendulum clocks stop Unstable objects
overturn or shift Open doors and windows are thrust open
and slam back again Liquids spill in small amounts from
well-filled open containers The sensation of vibration is like
that due to heavy objects falling inside the buildings
b) Slight damages in buildings of Type A are possible
c) Sometimes changes in flow of springs
VI Frightening
a) Felt by most indoors and outdoors Many people in buildings
are frightened and run outdoors A few persons loose their
balance Domestic animals run out of their stalls In few
instances dishes and glassware may break and books fall
down Heavy furniture may possibly move and small steeple
bells may ring
b) Damage of Grade 1 is sustained in single buildings of Type B
and in many of Type A Damage in few buildings of Type A
is of Grade 2
c) In few cases cracks up to widths of 1cm possible in wet
ground in mountains occasional landslips change in flow of
springs and in level of well water are observed
VII Damage of buildings
a) Most people are frightened and run outdoors Many find it
difficult to stand The vibration is noticed by persons driving
motor cars Large bells ring
b) In many buildings of Type C damage of Grade 1 is caused in
many buildings of Type B damage is of Grade 2 Most
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buildings of Type A suffer damage of Grade 3 few of Grade
4 In single instances landslides of roadway on steep slopes
crack inroads seams of pipelines damaged cracks in stone
walls
c) Waves are formed on water and is made turbid by mud stirred
up Water levels in wells change and the flow of springs
changes Sometimes dry springs have their flow resorted and
existing springs stop flowing In isolated instances parts of
sand and gravelly banks slip off
VIII Destruction of
buildings
a) Fright and panic also persons driving motor cars are
disturbed Here and there branches of trees break off Even
heavy furniture moves and partly overturns Hanging lamps
are damaged in part
b) Most buildings of Type C suffer damage of Grade 2 and few
of Grade 3 Most buildings of Type B suffer damage of Grade
3 Most buildings of Type A suffer damage of Grade 4
Occasional breaking of pipe seams Memorials and
monuments move and twist Tombstones overturn Stone
walls collapse
c) Small landslips in hollows and on banked roads on steep
slopes cracks in ground up to widths of several centimetres
Water in lakes becomes turbid New reservoirs come into
existence Dry wells refill and existing wells become dry In
many cases change in flow and level of water is observed
IX General damage of
buildings
a) General panic considerable damage to furniture Animals run
to and fro in confusion and cry
b) Many buildings of Type C suffer damage of Grade 3 and a
few of Grade 4 Many buildings of Type B show a damage of
Grade 4 and a few of Grade 5 Many buildings of Type A
suffer damage of Grade 5 Monuments and columns fall
Considerable damage to reservoirs underground pipes partly
broken In individual cases railway lines are bent and
roadway damaged
c) On flat land overflow of water sand and mud is often
observed Ground cracks to widths of up to 10 cm on slopes
and river banks more than 10 cm Furthermore a large
number of slight cracks in ground falls of rock many
landslides and earth flows large waves in water Dry wells
renew their flow and existing wells dry up
X General destruction of
building
a) Many buildings of Type C suffer damage of Grade 4 and a
few of Grade 5 Many buildings of Type B show damage of
Grade 5 Most of Type A have destruction of Grade 5
Critical damage to dykes and dams Severe damage to
bridges Railway lines are bent slightly Underground pipes
are bent or broken Road paving and asphalt show waves
b) In ground cracks up to widths of several centimetres
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sometimes up to 1m Parallel to water courses occur broad
fissures Loose ground slides from steep slopes From river
banks and steep coasts considerable landslides are possible
In coastal areas displacement of sand and mud change of
water level in wells water from canals lakes rivers etc
thrown on land New lakes occur
XI Destruction
a) Severe damage even to well built buildings bridges water
dams and railway lines Highways become useless
Underground pipes destroyed
b) Ground considerably distorted by broad cracks and fissures
as well as movement in horizontal and vertical directions
Numerous landslips and falls of rocks The intensity of the
earthquake requires to be investigated specifically
XII Landscape changes
a) Practically all structures above and below ground are greatly
damaged or destroyed
b) The surface of the ground is radically changed Considerable
ground cracks with extensive vertical and horizontal
movements are observed Falling of rock and slumping of
river banks over wide areas lakes are dammed waterfalls
appear and rivers are deflected The intensity of the
earthquake requires to be investigated specially
442 तवतभनन सकलो ो की िीवरिा मलो ो की िलना Comparison of Intensity Values of
Different Scales
443 तवतभनन पररमाण और िीवरिा क भको प का परभाव Effect of Earthquake of various
Magnitude and Intensity
The following describes the typical effects of earthquakes of various magnitudes near the
epicenter The values are typical only They should be taken with extreme caution since intensity
and thus ground effects depend not only on the magnitude but also on the distance to the
epicenter the depth of the earthquakes focus beneath the epicenter the location of the epicenter
and geological conditions (certain terrains can amplify seismic signals)
Fig 45 Comparison of Intensity Values of Different Scales
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Magnitude Description Mercalli
intensity
Average earthquake effects Average
frequency of
occurrence
(estimated)
10-19 Micro I Micro earthquakes not felt or felt rarely
Recorded by seismographs
Continualseveral
million per year
20-29 Minor I to II Felt slightly by some people No damage to
buildings
Over one million
per year
30-39 III to IV Often felt by people but very rarely causes
damage Shaking of indoor objects can be
noticeable
Over 100000 per
year
40-49 Light IV to VI Noticeable shaking of indoor objects and
rattling noises Felt by most people in the
affected area Slightly felt outside
Generally causes none to minimal damage
Moderate to significant damage very
unlikely Some objects may fall off shelves
or be knocked over
10000 to 15000
per year
50-59 Moderate VI to
VIII
Can cause damage of varying severity to
poorly constructed buildings At most none
to slight damage to all other buildings Felt
by everyone
1000 to 1500 per
year
60-69 Strong VII to X Damage to a moderate number of well-built
structures in populated areas Earthquake-
resistant structures survive with slight to
moderate damage Poorly designed
structures receive moderate to severe
damage Felt in wider areas up to hundreds
of mileskilometers from the epicenter
Strong to violent shaking in epicentral area
100 to 150 per
year
70-79 Major VIII or
Greater
Causes damage to most buildings some to
partially or completely collapse or receive
severe damage Well-designed structures
are likely to receive damage Felt across
great distances with major damage mostly
limited to 250 km from epicenter
10 to 20 per year
80-89 Great Major damage to buildings structures
likely to be destroyed Will cause moderate
to heavy damage to sturdy or earthquake-
resistant buildings Damaging in large
areas Felt in extremely large regions
One per year
90 and
greater
At or near total destruction ndash severe damage
or collapse to all buildings Heavy damage
and shaking extends to distant locations
Permanent changes in ground topography
One per 10 to 50
years
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45 भको प तनगरानी और सवाओो क तलए एजतसयो ो Agencies for Earthquake Monitoring and
Services
Centre for Seismology (CS) in Indian Meteorological Department (IMD) under Ministry of
Earth Sciences is nodal agency of Government of India dealing with various activities in
the field of seismology and allied disciplines and is responsible for monitoring seismic
activity in and around the country
The major activities currently being pursued by the Centre for Seismology (CS) include
a) Earthquake monitoring on 24X7 basis including real time seismic monitoring for early
warning of tsunamis
b) Operation and maintenance of national seismological network and local networks
c) Seismological data centre and information services
d) Seismic hazard and risk related studies
e) Field studies for aftershock swarm monitoring site response studies
f) Earthquake processes and modelling etc
These activities are being managed by various unitsgroups of the Centre for Seismology
(CS) as detailed below
1) Centre for Seismology (CS) is maintaining a country wide National Seismological
Network (NSN) consisting of a total of 82 seismological stations spread over the
entire length and breadth of the country This includes
a) 16-station V-SAT based digital seismic telemetry system around National Capital
Territory (NCT) of Delhi
b) 20-station VSAT based real time seismic monitoring network in North East region
of the country
(c) 17-station Real Time Seismic Monitoring Network (RTSMN) to monitor and
report large magnitude under-sea earthquakes capable of generating tsunamis on
the Indian coastal regions
2) The remaining stations are of standalone analog type
3) A Control Room is in operation on a 24X7 basis at premises of IMD Headquarters in
New Delhi with state-of-the art facilities for data collection processing and
dissemination of information to the concerned user agencies
4) India represented by CSIMD is a permanent Member of the International
Seismological Centre (ISC) UK
5) Seismological Bulletins of CSIMD are shared regularly with International
Seismological Centre (ISC) UK for incorporation in the ISCs Monthly Seismological
Bulletins which contain information on earthquakes occurring all across the globe
6) Towards early warning of tsunamis real-time continuous seismic waveform data of
three IMD stations viz Portblair Minicoy and Shillong is shared with global
community through IRIS (Incorporated Research Institutions of Seismology)
Washington DC USA
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अधयाय Chapter ndash 5
भवन म भको प परतिरोध म सधार क तलए सामानय तसदाोि General Principle for improving Earthquake Resistance in Building
51 िलकापन Lightness
Since the earthquake force is a function of mass the building should be as light as possible
consistent with structural safety and functional requirements Roofs and upper storeys of
buildings in particular should be designed as light as possible
52 तनमायण की तनरोिरिा Continuity of Construction
As far as possible all parts of the building should be tied together in such a manner that
the building acts as one unit
For integral action of building roof and floor slabs should be continuous throughout as
far as possible
Additions and alterations to the structures should be accompanied by the provision of
positive measures to establish continuity between the existing and the new construction
53 परोजककटोग एवो ससिि पाटटयस Projecting and Suspended Parts
Projecting parts should be avoided as far as possible If the projecting parts cannot be
avoided they should be properly reinforced and firmly tied to the main structure
Ceiling plaster should preferably be avoided When it is unavoidable the plaster should
be as thin as possible
Suspended ceiling should be avoided as far as possible Where provided they should be
light and adequately framed and secured
54 भवन की आकति Shape of Building
In order to minimize torsion and stress concentration the building should have a simple
rectangular plan
It should be symmetrical both with respect to mass and rigidity so that the centre of mass
and rigidity of the building coincide with each other
It will be desirable to use separate blocks of rectangular shape particularly in seismic
zones V and IV
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55 सतवधा जनक तबकडोग लआउट Preferred Building Layouts
Buildings having plans with shapes like L T E and Y shall preferably be separated into
rectangular parts by providing separation sections at appropriate places Typical examples are
shown in Fig 51
56 तवतभनन तदशाओो म शककत Strength in Various Directions
The structure shall have adequate strength against earthquake effects along both the horizontal
axes considering the reversible nature of earthquake forces
57 नी ोव Foundations
For the design of foundations the provisions of IS 1904 1986 in conjunctions with IS
1893 1984 shall generally be followed
The sub-grade below the entire area of the building shall preferably be of the same type of
the soil Wherever this is not possible a suitably located separation or crumple section shall
be provided
Loose fine sand soft silt and expansive clays should be avoided If unavoidable the
building shall rest either on a rigid raft foundation or on piles taken to a firm stratum
However for light constructions the following measures may be taken to improve the soil
on which the foundation of the building may rest
a) Sand piling and b) Soil stabilization
Structure shall not be founded on loose soil which will subside or liquefy during an
earthquake resulting in large differential settlement
58 छि एवो मोतजल Roofs and Floors
581 सपाट छि या फशय Flat roof or floor
Flat roof or floor shall not preferably be made of terrace of ordinary bricks supported on steel
timber or reinforced concrete joists nor they shall be of a type which in the event of an
earthquake is likely to be loosened and parts of all of which may fall If this type of construction
cannot be avoided the joists should be blocked at ends and bridged at intervals such that their
spacing is not altered during an earthquake
Fig 51 Typical Shapes of Building with Separation Sections [IS 4326 1993]
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582 ढलान वाली छि Pitched Roofs
For pitched roofs corrugated iron or asbestos sheets should be used in preference to
country Allahabad or Mangalore tiles or other loose roofing units
All roofing materials shall be properly tied to the supporting members
Heavy roofing materials should generally be avoided
583 सोवि छि Pent Roofs
All roof trusses should be supported on and fixed to timber band reinforced concrete band or
reinforced brick band The holding down bolts should have adequate length as required for
earthquake and wind forces
Where a trussed roof adjoins a masonry gable the ends of the purlins should be carried on and
secured to a plate or bearer which should be adequately bolted to timber reinforced concrete or
reinforced brick band at the top of gable end masonry
- At tie level all the trusses and the gable end should be provided with diagonal braces in plan
so as to transmit the lateral shear due to earthquake force to the gable walls acting as shear
walls at the ends
NOTE ndash Hipped roof in general have shown better structural behaviour during earthquakes than gable
ended roofs
584 जक मिराब Jack Arches
Jack arched roofs or floors where used should be provided with mild steel ties in all spans along
with diagonal braces in plan to ensure diaphragm actions
59 सीतढ़याो Staircases
The interconnection of the stairs with the adjacent floors should be appropriately treated by
providing sliding joints at the stairs to eliminate their bracing effect on the floors
Ladders may be made fixed at one end and freely resting at the other
Large stair halls shall preferably be separated from rest of the building by means of
separation or crumple section
Three types of stair construction may be adopted as described below
591 अलग सीतढ़याो Separated Staircases
One end of the staircase rests on a wall and the other end is carried by columns and beams which
have no connection with the floors The opening at the vertical joints between the floor and the
staircase may be covered either with a tread plate attached to one side of the joint and sliding on
the other side or covered with some appropriate material which could crumple or fracture during
an earthquake without causing structural damage
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The supporting members columns or walls are
isolated from the surrounding floors by means of
separation or crumple sections A typical
example is shown in Fig 52
592 तबलट-इन सीतढ़याो Built-in Staircase
When stairs are built monolithically with floors they can be protected against damage by
providing rigid walls at the stair opening An arrangement in which the staircase is enclosed by
two walls is given in Fig 53 (a) In such cases the joints as mentioned in respect of separated
staircases will not be necessary
The two walls mentioned above enclosing the staircase shall extend through the entire height of
the stairs and to the building foundations
Fig 53 (a) Rigidly Built-In Staircase [IS 4326 1993]
Fig 52 Separated Staircase
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593 सलाइतिोग जोड़ो ो वाली सीतढ़याो Staircases with Sliding Joints
In case it is not possible to provide rigid walls around stair openings for built-in staircase or to
adopt the separated staircases the staircases shall have sliding joints so that they will not act as
diagonal bracing (Fig 53 (b))
510 बॉकस परकार तनमायण Box Type Construction
This type of construction consists of prefabricated or in-situ masonry wall along with both the
axes of the building The walls support vertical loads and also act as shear walls for horizontal
loads acting in any direction All traditional masonry construction falls under this category In
prefabricated wall construction attention should be paid to the connections between wall panels
so that transfer of shear between them is ensured
511 अति सरकषा Fire Safety
Fire frequently follows an earthquake and therefore buildings should be constructed to make
them fire resistant in accordance with the provisions of relevant Indian Standards for fire safety
The relevant Indian Standards are IS 1641 1988 IS 1642 1989 IS 1643 1988 IS 1644 1988
and IS 1646 1986
Fig 53 (b) Staircase with Sliding Joint
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अधयाय Chapter ndash 6
भको प क दौरान आर सी भवनो ो क परदशयन पर सटरकचरल अतनयतमििाओो का परभाव Effect of Structural Irregularities on Performance of RC Buildings during Earthquakes
61 सटरकचरल अतनयतमििाओो का परभाव Effect of Structural Irregularities
There are numerous examples of past earthquakes in which the cause of failure of reinforced
concrete building has been ascribed to irregularities in configurations
Irregularities are mainly categorized as
(i) Horizontal Irregularities
(ii) Vertical Irregularities
62 कषतिज अतनयतमििाएो Horizontal Irregularities
Horizontal irregularities refer to asymmetrical plan shapes (eg L- T- U- F-) or discontinuities
in the horizontal resisting elements (diaphragms) such as cut-outs large openings re-entrant
corners and other abrupt changes resulting in torsion diaphragm deformations stress
concentration
Table ndash 61 Definitions of Irregular Buildings ndash Plan Irregularities (Fig 61)
S
No
Irregularity Type and Description
(i) Torsion Irregularity To be considered when floor diaphragms are rigid in their own
plan in relation to the vertical structural elements that resist the lateral forces Torsional
irregularity to be considered to exist when the maximum storey drift computed with
design eccentricity at one end of the structures transverse to an axis is more than 12
times the average of the storey drifts at the two ends of the structure
Fig 61 (a)
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(ii) Re-entrant Corners Plan configurations of a structure and its lateral force resisting
system contain re-entrant corners where both projections of the structure beyond the re-
entrant corner are greater than 15 percent of its plan dimension in the given direction
Fig 61 (b)
(iii) Diaphragm Discontinuity Diaphragms with abrupt discontinuities or variations in
stiffness including those having cut-out or open areas greater than 50 percent of the
gross enclosed diaphragm area or changes in effective diaphragm stiffness of more than
50 percent from one storey to the next
Fig 61 (c)
(iv) Out-of-Plane Offsets Discontinuities in a lateral force resistance path such as out-of-
plane offsets of vertical elements
Fig 61 (d)
(v) Non-parallel Systems The vertical elements
resisting the lateral force are not parallel to or
symmetric about the major orthogonal axes or the
lateral force resisting elements
Fig 61 (e)
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63 ऊरधायधर अतनयतमििाएो Vertical Irregularities
Vertical irregularities referring to sudden change of strength stiffness geometry and mass result
in irregular distribution of forces and or deformation over the height of building
Table ndash 62 Definition of Irregular Buildings ndash Vertical Irregularities (Fig 62)
S
No
Irregularity Type and Description
(i) a) Stiffness Irregularity ndash Soft Storey A soft storey is one in which the lateral stiffness is
less than 70 percent of that in the storey above or less than 80 percent of the average lateral
stiffness of the three storeys above
b) Stiffness Irregularity ndash Extreme Soft Storey A extreme soft storey is one in which the
lateral stiffness is less than 60 percent of that in the storey above or less than 70 percent of
the average stiffness of the three storeys above For example buildings on STILTS will fall
under this category
Fig 62 (a)
(ii) Mass Irregularity Mass irregularity shall be considered to exist where the seismic weight
of any storey is more than 200percent of that of its adjacent storeys The irregularity need
not be considered in case of roofs
Fig 62 (b)
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(iii) Vertical Geometric Irregularity Vertical geometric irregularity shall be considered to
exist where the horizontal dimension of the lateral force resisting system in any storey is
more than150 percent of that in its adjacent storey
Fig 62 (c)
(iv) In-Plane Discontinuity in Vertical Elements Resisting Lateral Force A in-plane offset of
the lateral force resisting elements greater than the length of those elements
Fig 62 (d)
(v) Discontinuity in Capacity ndash Weak Storey A weak storey is one in which the storey lateral
strength is less than 80 percent of that in the storey above The storey lateral strength is the
total strength of all seismic force resisting elements sharing the storey shear in the
considered direction
64 भवन तवनयास अतनयतमििाएो ndash सरसकयमए ववशलषण एव तनदमन क उपमय Building
Irregularities ndash Problems Analysis and Remedial Measures
The influence of irregularity on performance of building during earthquakes is presented to
account for the effects of these irregularities in analysis of problems and their solutions along
with the design
Vertical Geometric Irregularity when L2gt15 L1
In-Plane Discontinuity in Vertical Elements Resisting Weak Storey when Filt08Fi+ 1
Lateral Force when b gta
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Architectural problems Structural problems Remedial measures
Extreme heightdepth ratio
High overturning forces large drift causing non-structural damage foundation stability
Revive properties or special structural system
Extreme plan area Built-up large diaphragm forces Subdivide building by seismic joints
Extreme length depth ratio
Built-up of large lateral forces in perimeter large differences in resistance of two axes Experience greater variations in ground movement and soil conditions
Subdivide building by seismic joints
Variation in perimeter strength-stiffness
Torsion caused by extreme variation in strength and stiffness
Add frames and disconnect walls or use frames and lightweight walls
False symmetry Torsion caused by stiff asymmetric core Disconnect core or use frame with non-structural core walls
Re-entrant corners Torsion stress concentrations at the notches
Separate walls uniform box centre box architectural relief diagonal reinforcement
Mass eccentricities Torsion stress concentrations Reprogram or add resistance around mass to balance resistance and mass
Vertical setbacks and reverse setbacks
Stress concentration at notch different periods for different parts of building high diaphragm forces to transfer at setback
Special structural systems careful dynamic analysis
Soft storey frame Causes abrupt changes of stiffness at point of discontinuity
Add bracing add columns braced
Variation in column stiffness
Causes abrupt changes of stiffness much higher forces in stiffer columns
Redesign structural system to balance stiffness
Discontinuous shear wall Results in discontinuities in load path and stress concentration for most heavily loaded elements
Primary concern over the strength of lower level columns and connecting beams that support the load of discontinuous frame
Weak column ndash strong beam
Column failure occurs before beam short column must try and accommodate storey height displacement
Add full walls to reduce column forces or detach spandrels from columns or use light weight curtain wall with frame
Modification of primary structure
Most serious when masonry in-fill modifies structural concept creation of short stiff columns result in stress concentration
Detach in-fill or use light-weight materials
Building separation (Pounding)
Possibility of pounding dependent on building period height drift distance
Ensure adequate separation assuming opposite building vibrations
Coupled Incompatible deformation between walls and links
Design adequate link
Random Openings Seriously degrade capacity at point of maximum force transfer
Careful designing adequate space for reinforcing design
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अधयाय Chapter ndash 7
भवन की िायनातमक तवशषिाएा Dynamic Characteristics of Building
71 िायनातमक तवशषिाएा Dynamic Characteristics
Buildings oscillate during earthquake shaking The oscillation causes inertia force to be induced
in the building The intensity and duration of oscillation and the amount of inertia force induced
in a building depend on features of buildings called dynamic characteristics of building
The important dynamic characteristics of buildings are
a) Modes of Oscillation
b) Damping
A mode of oscillation of a building is defined by associated Natural Period and Deformed Shape
in which it oscillates Every building has a number of natural frequencies at which it offers
minimum resistance to shaking induced by external effects (like earthquakes and wind) and
internal effects(like motors fixed on it) Each of these natural frequencies and the associated
deformation shape of a building constitute a Natural Mode of Oscillation
The mode of oscillation with the smallest natural frequency (and largest natural period) is called
the Fundamental Mode the associated natural period T1is called the Fundamental Natural
Period
72 पराकतिक अवतध Natural Period
Natural Period (Tn) of a building is the time taken by it to undergo one complete cycle of
oscillation It is an inherent property of a building controlled by its mass m and stiffness k These
three quantities are related by
Its unit is second (s)
73 पराकतिक आवततत Natural Frequency
The reciprocal (1Tn) of natural period of a building is called the Natural Frequency fn its unit is
Hertz (Hz)
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74 पराकतिक अवतध को परभातवि करन वाल कारक Factors influencing Natural Period
741 कठोरिा का परभाव Effect of Stiffness Stiffer buildings have smaller natural period
742 दरवयमान का परभाव Effect of Mass Heavier buildings have larger natural period
743 कॉलम अतभतवनयास का परभाव Effect of Column Orientation Buildings with larger
column dimension oriented in the direction reduces the translational natural period of oscillation
in that direction
Fig 72 Effect of Mass
Fig 71 Effect of Stiffness
Fig 73 Effect of Column Orientation
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744 भवन की ऊो चाई का परभाव Effect of Building Height Taller buildings have larger
natural period
745 Unreinforced तचनाई भराव का परभाव Effect of Unreinforced Masonry Infills Natural
Period of building is lower when the stiffness contribution of URM infill is considered
Fig 75 Effect of Building Height
Fig 74 Effect of Building Height
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75 Mode आकति Mode Shape
Mode shape of oscillation associated with a natural period of a building is the deformed shape of
the building when shaken at the natural period Hence a building has as many mode shapes as
the number of natural periods
The deformed shape of the building associated with oscillation at fundamental natural period is
termed its first mode shape Similarly the deformed shapes associated with oscillations at
second third and other higher natural periods are called second mode shape third mode shape
and so on respectively
Fundamental Mode Shape of Oscillation
As shown in Fig 76 there are three basic modes of oscillation namely
1 Pure translational along X-direction
2 Pure translational along Y-direction and
3 Pure rotation about Z-axis
Regular buildings
These buildings have pure mode shapesThe Basic modes of oscillation ie two translational and
one rotational mode shapes
Irregular buildings
These buildings that have irregular geometry non-uniform distribution of mass and stiffness in
plan and along the height have mode shapes which are a mixture of these pure mode shapes
Each of these mode shapes is independent implying it cannot be obtained by combining any or
all of the other mode shapes
a) Fundamental and two higher translational modes of oscillation along X-direction of a
five storey benchmark building First modes shape has one zero crossing of the un-deformed
position second two and third three
Fig 76 Basic modes of oscillation
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b) Diagonal modes of oscillation First three modes of oscillation of a building symmetric in
both directions in plan first and second are diagonal translational modes and third rotational
c) Effect of modes of oscillation on column bending Columns are severely damaged while
bending about their diagonal direction
Fig 77 Fundamental and two higher translational modes of oscillation
along X-direction of a five storey benchmark building
Fig 78 Diagonal modes of oscillation
Fig 79 Effect of modes of oscillation on column bending
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76 Mode आकतियो ो को परभातवि करन वाल कारक Factors influencing Mode Shapes
761 Effect of relative flexural stiffness of structural elements Fundamental translational
mode shape changes from flexural-type to shear-type with increase in beam flexural stiffness
relative to that of column
762 Effect of axial stiffness of vertical members Fundamental translational mode shape
changes from flexure-type to shear-type with increase in axial stiffness of vertical members
Fig 710 Effect of relative flexural stiffness of structural elements
Fig 711 Effect of axial stiffness of vertical members
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763 Effect of degree of fixity at member ends Lack of fixity at beam ends induces flexural-
type behaviour while the same at column bases induces shear-type behaviour to the fundamental
translational mode of oscillation
Fig 712 Effect of degree of fixity at member ends
764 Effect of building height Fundamental translational mode shape of oscillation does not
change significantly with increase in building height unlike the fundamental translational natural
period which does change
Fig 713 Effect of building height
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765 Influence of URM Infill Walls in Mode Shape of RC frame Buildings Mode shape of
a building obtained considering stiffness contribution of URM is significantly different from that
obtained without considering the same
77 सोरचना की परतितकरया Response of Structure
The earthquakes cause vibratory motion which is cyclic about the equilibrium The structural
response is vibratory (Dynamic) and it is cyclic about the equilibrium position of structure The
fundamental natural frequency of most civil engineering structures lie in the range of 01 sec to
30 sec or so This is also the range of frequency content of earthquake-generated ground
motions Hence the ground motion imparts considerable amount of energy to the structures
Initially the structure responds elastically to the ground motion however as its yield capacity is
exceeded the structure responds in an inelastic manner During the inelastic response stiffness
and energy dissipation properties of the structure are modified
Response of the structure to a given strong ground motion depends not only on the properties of
input ground motion but also on the structural properties
78 तिजाइन सकटर म Design Spectrum
The design spectrum is a design specification which is arrived at by considering all aspects The
design spectrum may be in terms of acceleration velocity or displacement
Fig 714 Influence of URM Infill Walls in Mode Shape of RC frame Buildings
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Since design spectrum is a specification for design it cannot be viewed in isolation without
considering the other factors that go into the design process One must concurrently specify
a) The procedure to calculate natural period of the structure
b) The damping to be used for a given type of structure
c) The permissible stresses and strains load factors etc
Unless this information is part of a design spectrum the design specification is incomplete
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अधयाय Chapter ndash 8
डिजमइन पमशवा बलो क तनधमारण क ललए कोि आधमररि िरीकम Code based Procedure for Determination of Design Lateral Loads
81 भको पी तिजाइन की तफलोसफ़ी Philosophy of Seismic Design
Design of earthquake effect is not termed as Earthquake Proof Design Actual forces that appear
on structure during earthquake are much greater than the design forces Complete protection
against earthquake of all size is not economically feasible and design based alone on strength
criteria is not justified Earthquake demand is estimated only based on concept of probability of
exceedance Design of earthquake effect is therefore termed as Earthquake Resistant Design
against the probable value of demand
Maximum Considered Earthquake (MCE) The earthquake corresponding to the Ultimate
Safety Requirement is often called as Maximum Considered Earthquake
Design Basis Earthquake (DBE) It is defined as the Maximum Earthquake that reasonably can
be expected to experience at the site during lifetime of structure
The philosophy of seismic design is to ensure that structures possess at least a minimum strength
to
(i) resist minor (lt DBE) which may occur frequently without damage
(ii) resist moderate earthquake (DBE) without significant structural damage through some
non-structural damage
(iii) resist major earthquake (MCE) without collapse
82 भको पी तवशलषण क तलए िरीक Methods for Seismic Analysis
The response of a structure to ground vibrations is a function of the nature of foundation soil
materials form size and mode of construction of structures and duration and characteristics of
ground motion Code specifies design forces for structures standing on rock or firm soils which
do not liquefy or slide due to loss of strength during ground motion
Analysis is carried out by
a- Dynamic analysis procedure [Clause 78 of IS 1893 (Part I) 2002]
b- Simplified method referred as Lateral Force Procedure [Clause 75 of IS 1893 (Part I)
2002] also recognized as Equivalent Lateral Force Procedure or Equivalent Static
Procedure in the literature
The main difference between the equivalent lateral force procedure and dynamic analysis
procedure lies in the magnitude and distribution of lateral forces over the height of the buildings
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In the dynamic analysis procedure the lateral forces are based on the properties of the natural
vibration modes of the building which are determined by the distribution of mass and stiffness
over height In the equivalent lateral force procedures the magnitude of forces is based on an
estimation of the fundamental period and on the distribution of forces as given by simple
formulae appropriate for regular buildings
83 िायनातमक तवशलषण Dynamic Analysis
Dynamic analysis shall be performed to obtain the design seismic force and its distribution to
different levels along the height of the building and to the various lateral load resisting elements
for the following buildings
a) Regular buildings ndash Those greater than 40 m in height in Zones IV and V and those greater
than 90 m in height in Zones II and III Modelling as per Para 7845 of IS 1893 (Part 1)
2002 can be used
b) Irregular buildings (as defined in Table ndash 61 and Table ndash 62 of Chapter - 6) ndash All framed
buildings higher than 12m in Zones IV and V and those greater than 40m in height in Zones
II and III
84 पारशय बल परतकरया Lateral Force Procedure
The random earthquake ground motions which cause the structure to vibrate can be resolved in
any three mutually perpendicular directions The predominant direction of ground vibration is
usually horizontal
The codes represent the earthquake-induced inertia forces in the form of design equivalent static
lateral force This force is called as the Design Seismic Base Shear VB VB remains the primary
quantity involved in force-based earthquake-resistant design of buildings
The Design Seismic Base Shear VB is given by
Where Ah = Design horizontal seismic coefficient for a structure
=
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Z = Zone Factor
It is for the Maximum Considered Earthquake (MCE) and service life of structure in a zone
Generally Design Basis Earthquake (DBE) is half of Maximum Considered Earthquake
(MCE) The factor 2 in the denominator of Z is used so as to reduce the MCE zone factor to
the factor for DBE
The value of Ah will not be taken less than Z2 whatsoever the value of IR
The value of Zone Factor is given in Table ndash 81
Table ndash 81 Zone Factor Z[IS 1893 (Part 1) 2002]
Seismic Zone II III IV V
Seismic Intensity Low Moderate Severe Very Severe
Zone Factor Z 010 016 024 036
I = Importance Factor
Value of importance factor depends upon the functional use of the structures characterized
by hazardous consequences of its failure post-earthquake functional needs historical value
or economic importance (as given in Table ndash 82)
Table ndash 82 Importance Factors I [IS 1893 (Part 1) 2002]
S
No
Structure Importance
Factor
(i) Important service and community buildings such as hospitals schools
monumental structures emergency buildings like telephone exchange
television stations radio stations railway stations fire station buildings
large community halls like cinemas assembly halls and subway stations
power stations
15
(ii) AU other buildings 10
Note
1 The design engineer may choose values of importance factor I greater than those
mentioned above
2 Buildings not covered in S No (i) and (ii) above may be designed for higher value of I
depending on economy strategy considerations like multi-storey buildings having
several residential units
3 This does not apply to temporary structures like excavations scaffolding etc of short
duration
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R = Response Reduction Factor
To make normal buildings economical design code allows some damage for reducing the
cost of construction This philosophy is introduced with the help of Response reduction
factor R
The ratio (IR) shall not be greater than 10
Depending on the perceived seismic damage performance of the structure by ductile or brittle
deformations the values of R1)
for buildings are given in Table ndash 83 below
Table ndash 83 Response Reduction Factor1)
R for Building Systems [IS 1893 (Part 1) 2002]
S No Lateral Load Resisting System R Building Frame Systems (i) Ordinary RC moment-resisting frame ( OMRF )
2) 30
(ii) Special RC moment-resisting frame ( SMRF )3)
50 (iii) Steel frame with
a) Concentric braces 40 b) Eccentric braces 50
(iv) Steel moment resisting frame designed as per SP 6 (6) 50 Building with Shear Walls
4)
(v) Load bearing masonry wall buildings5)
a) Unreinforced 15 b) Reinforced with horizontal RC bands 25 c) Reinforced with horizontal RC bands and vertical bars at cornersof
rooms and jambs of openings 30
(vi) Ordinary reinforced concrete shear walls6)
30 (vii) Ductile shear walls
7) 40
Buildings with Dual Systems8)
(viii) Ordinary shear wall with OMRF 30 (ix) Ordinary shear wall with SMRF 40 (x) Ductile shear wall with OMRF 45 (xi) Ductile shear wall with SMRF 50 1) The values of response reduction factor are to be used for buildings with lateral load resisting
elements and not just for the lateral load resisting elements built in isolation 2) OMRF (Ordinary Moment-Resisting Frame) are those designed and detailed as per IS 456 or
IS 800 but not meeting ductile detailing requirement as per IS 13920 or SP 6 (6) respectively 3) SMRF (Special Moment-Resisting Frame) defined in 4152
As per 4152 SMRF is a moment-resisting frame specially detailed to provide ductile behaviour and comply with the requirements given in IS 4326 or IS 13920 or SP 6 (6)
4) Buildings with shear walls also include buildings having shear walls and frames but where a) frames are not designed to carry lateral loads or b) frames are designed to carry lateral loads but do not fulfil the requirements of lsquodual
systemsrsquo 5) Reinforcement should be as per IS 4326 6) Prohibited in zones IV and V 7) Ductile shear walls are those designed and detailed as per IS 13920 8) Buildings with dual systems consist of shear walls ( or braced frames ) and moment resisting
frames such that a) the two systems are designed to resist the total design force in proportion to their lateral
stiffness considering the interaction of the dual system at all floor levels and b) the moment resisting frames are designed to independently resist at least 25 percent of the
design seismic base shear
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Sag = Average Response Acceleration Coefficient
Net shaking of a building is a combined effect of the energy carried by the earthquake at
different frequencies and the natural period (T) of the building Code reflects this by
introducing a structural flexibility factor (Sag) also termed as Design Acceleration
Coefficient
Design Acceleration Coefficient (Sag) corresponding to 5 damping for different soil
types normalized to Peak Ground Acceleration (PAG) corresponding to natural period (T)
of structure considering soil structure interaction given by Fig 81 and associated expression
given below
Table ndash 84 gives multiplying factors for obtaining spectral values for various other damping
Table ndash 84 Multiplying Factors for Obtaining Values for Other Damping [IS 1893 (Part 1) 2002]
Damping () 0 2 5 7 10 15 20 25 30
Factors 320 140 100 090 080 070 060 055 050
85 को पन की मौतलक पराकतिक अवतध Fundamental Natural Period of Vibration
The approximate fundamental natural period of vibration (Ta)in seconds of a moment-resisting
frame building without brick infill panels may be estimated by the empirical expression
Ta = 0075 h075
for RC frame building
= 0085 h075
for steel frame building
Where h = Height of building in m This excludes the basement storeys where
basement walls are connected with the ground floor deck or fitted between
the building columns But it includes the basement storeys when they are
not so connected
Fig 81 Response Spectra for Rock and Soil Sitesfor5 Damping [IS 1893 (Part 1) 2002]
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The approximate fundamental natural period of vibration (Ta) in seconds of all other buildings
including moment-resisting frame buildings with brick infill panels may be estimated by the
empirical expression
Where h = Height of building in m as defined above
d = Base dimension of the building at the plinth level in m along the
considered direction of the lateral force
86 तिजाइन पारशय बल Design Lateral Force
The total design lateral force or design seismic base shear (VB) along any principal direction shall
be determined by the following expression
Where Ah= Design horizontal acceleration spectrum value as per 642 using the
fundamental natural period Ta as per 76 in the considered direction of
vibration and
W= Seismic weight of the building
The design lateral force shall first be computed for the building as a whole This design lateral
force shall then be distributed to the various floor levels
The overall design seismic force thus obtained at each floor level shall then be distributed to
individual lateral load resisting elements depending on the floor diaphragm action
87 तिजाइन बल का तविरण Distribution of Design Force
871 Vertical Distribution of Base Shear to Different Floor Levels
The Design Seismic Base Shear (VB) as computed above shall be distributed along the height of
the building as per the following expression
Where
Qi= Design lateral force at floor i
Wi = Seismic weight of floor i
hi = Height of floor i measured from base and
n= Number of storeys in the building is the number of levels at which the masses are
located
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872 Distribution of Horizontal Design Lateral Force to Different Lateral Force Resisting
Elements
1 In case of buildings whose floors are capable of providing rigid horizontal diaphragm
action the total shear in any horizontal plane shall be distributed to the various vertical
elements of lateral force resisting system assuming the floors to be infinitely rigid in the
horizontal plane
2 In case of building whose floor diaphragms cannot be treated as infinitely rigid in their
own plane the lateral shear at each floor shall be distributed to the vertical elements
resisting the lateral forces considering the in-plane flexibility of the diaphragms
Notes
1 A floor diaphragm shall be considered to be flexible if it deforms such that the maximum
lateral displacement measured from the chord of the deformed shape at any point of the
diaphragm is more than 15 times the average displacement of the entire diaphragm
2 Reinforced concrete monolithic slab-beam floors or those consisting of prefabricated
precast elements with topping reinforced screed can be taken rigid diaphragms
88 तिजाइन उदािरण Design Example ndash To determine Base Shear and its distribution
along Height of Building
Exercise ndash 1 Determine the total base shear as per IS 1893(Part 1)2002 and distribute the base
shear along the height of building to be used as school building in Bhuj Gujrat and founded on
Medium Soil Basic parameters for design of building are as follows
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ELEVATION
Solution
Basic Data
Following basic data is considered for analysis
i) Grade of Concrete M-25
ii) Grade of Steel Fe ndash 415 Tor Steel
iii) Density of Concrete 25 KNm3
iv) Density of Brick Wall 20 KNm3
v) Live Load for Roof 15 KNm2
vi) Live Load for Floor 50 KNm2
vii) Slab Thickness 150 mm
viii) Beam Size
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(a) 500 m Span 250 mm X 600 mm
(b) 400 m Span 250 mm X 550 mm
(c) 200 m Span 250 mm X 400 mm
ix) Column Size
(a) For 500 m Span 300 mm X 600 mm
(b) For 200 m Span 300 mm X 500 mm
Load Calculations
1 Dead Load Building is of G+4 Storeys
Approximate Covered Area of Building on GF = 30 X 8 = 240 m2
Approximate Covered Area of 1st 2
nd 3
rd amp 4
th Floor = 240 m
2
Total Floor Area = 5 X 240 = 1200 m2
Roof Area = 1 X 240 = 240 m2
(I) Slab
Self Wt of Slab = 015 X 25 = 375 KNm2
Wt of Floor Finish = 125 KNm2
------------------------------
Total = 500 KNm2
Dead Load of Slab per Floor = 240 X 5 = 1200 KN
Dead Load of Slab on Roof = 240 X 5 = 1200 KN
(II) Beam
Wt per m of 250 X 600 mm beam = 025 X 060 X 25 = 375 KNm
Wt per m of 250 X 550 mm beam = 025 X 055 X 25 = 344 KNm
Wt per m of 250 X 400 mm beam = 025 X 040 X 25 = 250 KNm
Weight of Beam per Floor
= (2 X 30 X 375) + (4 X 6 + 30) X 344 + (2 X 6 X 250)
= 225 + 18576 + 30 = 44076 KN [Say 44100 KN]
(III) Column
Wt per m of 300 X 600 mm column = 030 X 060 X 25 = 450 KNm
Wt per m of 300 X 500 mm column = 030 X 050 X 25 = 375 KNm
Weight of Column per Floor
= (12 X 3 X 450) + (6 X 3 X 375)
= 162 + 6750 = 22950 KN [Say 23000 KN]
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Walls
250 mm thick wall (including plaster) are provided Assuming 20 opening in the
wall ndash
Wt of Wall per m = 025 X 080 X 20 X 250
Wall Thickness Reduction Density Clear Height
= 1000 KNm
Wt of Parapet Wall per m = 0125 X 20 X 100 = 250 KNm
Wall Thickness Density Clear Height
Wt of Wall per Floor = 1000 X [30 X 3 + 2 X 2] = 940 KN
Wt of Wall at Roof = 250 X [30 X 2 + 8 X 2] = 190 KN
Total Dead Load ndash
(i) For Floor = Slab + Beam + Column + Wall
= 1200 + 441 + 230 + 940 = 2811 KN
(ii) For Roof = 1200 + 441 + 190 = 1831 KN
Slab Beam Parapet
2 Live Load Live Load on Floor = 40 KNm2
As per Table ndash 8 in Cl 731 of IS 1893 (Part 1)2002 ldquoage of Imposed Load to be
considered in Seismic Weight calculationrdquo
(i) Up to amp including 300 KNm2 = 25
(ii) Above 300 KNm2 = 50
Live Load on Floors to be = 200 KNm2 [ie 50 of 40 KNm
2]
considered for Earthquake Force
As per Cl 732 of IS 1893 (Part 1)2002 for calculating the design seismic force of the
structure the imposed load on roof need not be considered
Therefore Live Load on Roof = 000 KN
Seismic Weight due to Live Load
(i) For Floor = 240 X 2 = 480 KN
(ii) For Roof = 000 KN
3 Seismic Weight of Building
As per Cl 74 of IS 1893 (Part 1)2002
(i) For Floor = DL of Floor + LL on Floor
= 2811 + 480 = 3291 KN
(ii) For Roof = 1831 + 000 = 1831 KN
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58
Total Seismic Weight of Building = 5 X 3291 + 1 X 1831
W = 18286 KN
4 Determination of Base Shear
As per Cl 75 of IS 1893 (Part 1)2002 VB = Ah W
Where
VB = Base Shear
Ah = Design Horizontal Acceleration Spectrum
=
W = Seismic Wt of Building
Total height of Building above Ground Level = 1500 m
As per Cl 76 of IS 1893 (Part 1)2002 Fundamental Natural Period of Vibration for RC
Frame Building is
Ta = 0075 h075
= 0075 (15)075
= 0572 Sec
Average Response Acceleration Coefficient = 25
for 5 damping and Type II soil
Bhuj Gujrat is in Seismic Zone V
As per Table ndash 2 of IS 1893 (Part 1)2002
Zone Factor Z = 036
As per Table ndash 6 of IS 1893 (Part 1)2002
Impedance Factor I = 150
As per Table ndash 7 of IS 1893 (Part 1)2002
Response Reduction Factor for Ordinary R = 300
RC Moment-resisting Frame (OMRF) Building
Ah =
= (0362) X (1530) X (25)
= 0225
Base Shear VB = Ah W
= 0225 X 18286
= 411435 KN [Say 411400 KN]
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5 Vertical Distribution of Base Shear to Different Floors Levels
As per Cl 771 of IS 1893 (Part 1)2002
Where
Qi= Design lateral force at floor i
Wi = Seismic weight of floor i
hi = Height of floor i measured from base and
n= Number of storeys in the building is the number of levels at which the masses are
located
VB = 4114 KN
Storey
No
Mass
No
Wi hi Wi hi2
f =
Qi = VB x f
(KN)
Vi
(KN)
Roof 1 1831 18 593244 0268 1103 1103
4th
Floor 2 3291 15 740475 0333 1370 2473
3rd
Floor 3 3291 12 473904 0213 876 3349
2nd
Floor 4 3291 9 266571 0120 494 3843
1st Floor 5 3291 6 118476 0053 218 4061
Ground 6 3291 3 29619 0013 53 4114
= 2222289
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60
अधयाय Chapter ndash 9
ढााचागि सोरचना का तनमायण Construction of Framed Structure
91 गरतवाकषयण लोतिोग और भको प लोतिोग म आर सी तबकडोग का वयविार Behaviour of RC
Building in Gravity Loading and Earthquake Loading
In recent times reinforced concrete buildings have become common in India particularly in
towns and cities A typical RC building consists of horizontal members (beams and slabs) and
vertical members (columns and walls) The system is supported by foundations that rest on
ground The RC frame participates in resisting the gravity and earthquake forces as illustrated in
Fig 91
Gravity Loading
1 Load due to self weight and contents on buildings cause RC frames to bend resulting in
stretching and shortening at various locations
2 Tension is generated at surfaces that stretch
and compression at those that shorten
3 Under gravity loads tension in the beams is
at the bottom surface of the beam in the
central location and is at the top surface at
the ends
Earthquake Loading
1 It causes tension on beam and column faces
at locations different from those under
gravity loading the relative levels of this
tension (in technical terms bending
moment) generated in members are shown
in Figure
2 The level of bending moment due to
earthquake loading depends on severity of
shaking and can exceed that due to gravity
loading
3 Under strong earthquake shaking the beam
ends can develop tension on either of the
top and bottom faces
4 Since concrete cannot carry this tension
steel bars are required on both faces of
beams to resist reversals of bending
moment
5 Similarly steel bars are required on all faces of columns too
Fig 91 Earthquake shaking reverses tension and
compression in members ndash reinforcement is
required on both faces of members
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92 परबतलि को करीट इमारिो ो पर कषतिज भको प का परभाव Effect of Horizontal Earthquake Force
on RC Buildings
Earthquake shaking generates inertia forces in the building which are proportional to the
building mass Since most of the building mass is present at floor levels earthquake-induced
inertia forces primarily develop at the floor
levels These forces travel downwards -
through slab and beams to columns and walls
and then to the foundations from where they
are dispersed to the ground (Fig 92)
As inertia forces accumulate downwards from
the top of the building the columns and walls
at lower storeys experience higher earthquake-
induced forces and are therefore designed to be
stronger than those in storeys above
93 कषमिा तिजाइन सोकलपना Capacity Design Concept
(i) Let us take two bars of same length amp Cross-sectional area
1st bar ndash Made up of Brittle Material
2nd
bar ndash Made up of Ductile Material
(ii) Pull both the bars until they break
(iii) Plot the graph of bar force F versus bar
elongation Graph will be as given in Fig
93
(iv) It is observed that ndash
a) Brittle bar breaks suddenly on reaching its
maximum strength at a relatively small
elongation
b) Ductile bar elongates by a large amount
before it breaks
Materials used in building construction are steel
masonry and concrete Steel is ductile material
while masonry and concrete are brittle material
Capacity design concept ensures that the brittle
element will remain elastic at all loads prior to the
failure of ductile element Thus brittle mode of
failure ie sudden failure has been prevented
Fig 92 Total horizontal earthquake force in a
building increase downwards along its height
Fig 93 Tension Test on Materials ndash ductile
versus brittle materials
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The concept of capacity design is used to ensure post-yield ductile behaviour of a structure
having both ductile and brittle elements In this method the ductile elements are designed and
detailed for the design forces Then an upper-bound strength of the ductile elements is obtained
It is then expected that if the seismic force keeps increasing a point will come when these ductile
elements will reach their upper-bound strength and become plastic Clearly it is necessary to
ensure that even at that level of seismic force the brittle elements remain safe
94 लचीलापन और ऊजाय का अपवयय Ductility and Energy Dissipation
From strength point of view overdesigned structures need not necessarily demonstrate good
ductility By ductility of Moment Resisting Frames (MRF) one refers to the capacity of the
structure and its elements to undergo large deformations without loosing either strength or
stiffness It is important for a building in a seismic zone to be resilient ie absorb the shock from
the ground and dissipate this energy uniformly throughout the structure
In MRFs the dissipation of the input seismic energy takes place in the form of flexural yielding
and resulting in the formation of plastic moment hinges Due to cyclic nature of the flexural
effects both positive and negative plastic moment hinges may be formed
95 मजबि सतोभ ndash कमजोर बीम फलोसफ़ी lsquoStrong Column ndash Weak Beamrsquo Philosophy
Because beams are usually capable of developing large ductility than columns which are
subjected to significant compressive loads many building frames are designed based on the
lsquostrong column ndash weak beamrsquo philosophy Figure shows that for a frame designed according to
the lsquostrong column ndash weak beamrsquo philosophy to form a failure mechanism many more plastic
hinges have to be formed than a
frame designed according to the
ldquoweak column ndash strong beamrsquo
philosophy The frames designed
by the former approach dissipate
greater energy before failure
When this strategy is adopted in
design damage is likely to occur
first in beams When beams are
detailed properly to have large
ductility the building as a whole
can deform by large amounts
despite progressive damage caused
due to consequent yielding of
beams
Note If columns are made weaker they suffer severe local damage at the top and bottom of a
particular storey This localized damage can lead to collapse of a building although columns at
storeys above remain almost undamaged (Fig 94)
Fig 94 Two distinct designs of buildings that result in different
earthquake performancesndashcolumns should be stronger than beams
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For a building to remain safe during earthquake shaking columns (which receive forces from
beams) should be stronger than beams and foundations (which receive forces from columns)
should be stronger than columns
96 कठोर िायाफराम तकरया Rigid Diaphragm Action
When beams bend in the vertical direction during earthquakes these thin slabs bend along with them And when beams move with columns in the horizontal direction the slab usually forces the beams to move together with it In most buildings the geometric distortion of the slab is negligible in the horizontal plane this behaviour is known as the rigid diaphragm action This aspect must be considered during design (Fig 95)
97 सॉफट सटोरी तबकडोग क साथ ndash ओपन गराउोि सटोरी तबकडोग जो तक भको प क समय कमजोर िोिी ि
Building with Soft storey ndash Open Ground Storey Building that is vulnerable in
Earthquake
The buildings that have been constructed in recent times with a special feature - the ground storey is left open for the purpose of parking ie columns in the ground storey do not have any partition walls (of either masonry or RC) between them are called open ground storey buildings or buildings on stilts
An open ground storey building (Fig 96) having only columns in the ground storey and both partition walls and columns in the upper storeys have two distinct characteristics namely
(a) It is relatively flexible in the ground storey ie the relative horizontal displacement it undergoes in the ground storey is much larger than what each of the storeys above it does This flexible ground storey is also called soft storey
(b) It is relatively weak in ground storey ie
the total horizontal earthquake force it can carry in the ground storey is significantly smaller than what each of the storeys above it can carry Thus the open ground storey may also be a weak storey
Fig 95 Floor bends with the beam but moves all
columns at that level together
Fig 96 Upper storeys of open ground storey building
move together as a single block ndash such buildings are
like inverted pendulums
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The collapse of more than a hundred RC frame buildings with open ground storeys at
Ahmedabad (~225km away from epicenter) during the 2001 Bhuj earthquake has emphasized
that such buildings are extremely vulnerable under earthquake shaking
After the collapses of RC buildings in 2001 Bhuj earthquake the Indian Seismic Code IS 1893
(Part 1) 2002 has included special design provisions related to soft storey buildings
Firstly it specifies when a building should be considered as a soft and a weak storey building
Secondly it specifies higher design forces for the soft storey as compared to the rest of the
structure
The Code suggests that the forces in the columns
beams and shear walls (if any) under the action of
seismic loads specified in the code may be
obtained by considering the bare frame building
(without any infills) However beams and
columns in the open ground storey are required to
be designed for 25 times the forces obtained
from this bare frame analysis (Fig 97)
For all new RC frame buildings the best option is
to avoid such sudden and large decrease in stiffness
andor strength in any storey it would be ideal to
build walls (either masonry or RC walls) in the
ground storey also Designers can avoid dangerous
effects of flexible and weak ground storeys by
ensuring that too many walls are not discontinued
in the ground storey ie the drop in stiffness and
strength in the ground storey level is not abrupt due
to the absence of infill walls (Fig 98)
The existing open ground storey buildings need to be strengthened suitably so as to prevent them
from collapsing during strong earthquake shaking The owners should seek the services of
qualified structural engineers who are able to suggest appropriate solutions to increase seismic
safety of these buildings
971 भरी हई दीवार In-Fill Walls
When columns receive horizontal forces at floor
levels they try to move in the horizontal direction
but masonry walls tend to resist this movement
Due to their heavy weight and thickness these
walls attract rather large horizontal forces
However since masonry is a brittle material these
walls develop cracks once their ability to carry
horizontal load is exceeded Thus infill walls act
like sacrificial fuses in buildings they develop
Fig 99 Infill walls move together with the
columns under earthquake shaking
Fig 97 Open ground storey building ndashassumptions
made in current design practice are not consistent
with the actual structure
Fig 98 Avoiding open ground storey problem ndash
continuity of walls in ground storey is preferred
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65
cracks under severe ground shaking but help share the load of the beams and columns until
cracking Earthquake performance of infill walls is enhanced by mortars of good strength
making proper masonry courses and proper packing of gaps between RC frame and masonry
infill walls (Fig 99)
98 भको प क दौरान लघ कॉलम वाली इमारिो ो का वयविार Behavior of Buildings with Short
Columns during Earthquakes
During past earthquakes reinforced concrete (RC) frame buildings that have columns of different heights within one storey suffered more damage in the shorter columns as compared to taller columns in the same storey
Two examples of buildings with short columns are shown in Fig 910 ndash (a) buildings on a sloping ground and (b) buildings with a mezzanine floor
Poor behaviour of short columns is due to the fact that in an earthquake a tall column and a short column of same cross-section move horizontally by same amount
However the short column is stiffer as compared
to the tall column and it attracts larger earthquake
force Stiffness of a column means resistance to
deformation ndash the larger is the stiffness larger is
the force required to deform it If a short column is
not adequately designed for such a large force it
can suffer significant damage during an
earthquake This behaviour is called Short Column
Effect (Fig 911)
In new buildings short column effect should be
avoided to the extent possible during architectural
design stage itself When it is not possible to avoid
short columns this effect must be addressed in
structural design The IS13920-1993for ductile
detailing of RC structures requires special
confining reinforcement to be provided over the
full height of columns that are likely to sustain
short column effect
Fig 910 Buildings with short columns ndash two
explicit examples of common occurrences
Fig 911 Short columns are stiffer and attract larger
forces during earthquakes ndash this must be accounted
for in design
Fig 912 Details of reinforcement in a building with
short column effect in some columns ndashadditional
special requirements are given in IS13920- 1993 for
the short columns
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The special confining reinforcement (ie closely spaced closed ties) must extend beyond the
short column into the columns vertically above and below by a certain distance as shown in
Fig 912
In existing buildings with short columns different retrofit solutions can be employed to avoid
damage in future earthquakes Where walls of partial height are present the simplest solution is
to close the openings by building a wall of full height ndash this will eliminate the short column
effect If that is not possible short columns need to be strengthened using one of the well
established retrofit techniques The retrofit solution should be designed by a qualified structural
engineer with requisite background
99 भको प परतिरोधी इमारिो ो की लचीलापन आवशयकिाएा Ductility requirements of
Earthquake Resistant Buildings
The primary members of structure such as beams and columns are subjected to stress reversals
from earthquake loads The reinforcement provided shall cater to the needs of reversal of
moments in beams and columns and at their junctions
Earthquake motion often induces forces large enough to cause inelastic deformations in the
structure If the structure is brittle sudden failure could occur But if the structure is made to
behave ductile it will be able to sustain the earthquake effects better with some deflection larger
than the yield deflection by absorption of energy Therefore besides the design for strength of
the frame ductility is also required as an essential element for safety from sudden collapse during
severe shocks
The ductility requirements will be deemed to be satisfied if the conditions given as in the
following are achieved
1 For all buildings which are more than 3 storeys in height the minimum grade of concrete
shall be M20 ( fck = 20 MPa )
2 Steel reinforcements of grade Fe 415 (IS 1786 1985) or less only shall be used
However high strength deformed steel bars produced by the thermo-mechanical treatment
process of grades Fe 500 and Fe 550 having elongation more than 145 percent and conforming
to other requirements of IS 1786 1985 may also be used for the reinforcement
910 बीम तजनह आर सी इमारिो ो म भको प बलो ो का तवरोध करन क तलए िाला जािा ि Beams that
are required to resist Earthquake Forces in RC Buildings
In RC buildings the vertical and horizontal members (ie the columns and beams) are built
integrally with each other Thus under the action of loads they act together as a frame
transferring forces from one to another
Beams in RC buildings have two sets of steel reinforcement (Fig 913) namely
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67
(a) long straight bars (called longitudinal bars)
placed along its length and
(b) closed loops of small diameter steel bars (called
stirrups)placed vertically at regular intervals
along its full length
Beams sustain two basic types of failures namely
(i) Flexural (or Bending) Failure
As the beam sags under increased loading it can
fail in two possible ways (Fig 914)
If relatively more steel is present on the tension
face concrete crushes in compression this is
a brittle failure and is therefore undesirable
If relatively less steel is present on the
tension face the steel yields first (it keeps
elongating but does not snap as steel has
ability to stretch large amounts before it
snaps and redistribution occurs in the beam
until eventually the concrete crushes in
compression this is a ductile failure and
hence is desirable Thus more steel on
tension face is not necessarily desirable The
ductile failure is characterized with many
vertical cracks starting from the stretched
beam face and going towards its mid-depth
(ii) Shear Failure
A beam may also fail due to shearing action A shear crack is inclined at 45deg to the horizontal it
develops at mid-depth near the support and grows towards the top and bottom faces Closed loop
stirrups are provided to avoid such shearing action Shear damage occurs when the area of these
stirrups is insufficient Shear failure is brittle and therefore shear failure must be avoided in the
design of RC beams
Longitudinal bars are provided to resist flexural
cracking on the side of the beam that stretches
Since both top and bottom faces stretch during
strong earthquake shaking longitudinal steel bars
are required on both faces at the ends and on the
bottom face at mid-length (Fig 915)
Fig 914 Two types of damage in a beam flexure
damage is preferred Longitudinal bars resist the
tension forces due to bending while vertical stirrups
resist shear forces
Fig 913 Steel reinforcement in beams ndash stirrups
prevent longitudinal bars from bending outwards
Fig 915 Location and amount of longitudinal steel
bars in beams ndash these resist tension due to flexure
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Designing a beam involves the selection of its material properties (ie grades of steel bars
and concrete) and shape and size these are usually selected as a part of an overall design
strategy of the whole building
The amount and distribution of steel to be provided in the beam must be determined by
performing design calculations as per IS 456-2000 and IS 13920-1993
911 फलकसचरल ममबसय क तलए सामानय आवशयकिाएा General Requirements for Flexural
Members
These members shall satisfy the following requirements
The member shall preferably have a width-to-depth ratio of more than 03
The width of the member shall not be less than 200 mm
The depth D of the member shall preferably be not more than 14 of the clear span
The factored axial stress on the member under earthquake loading shall not exceed 01fck
9111 अनदधयय सदढीकरण Longitudinal Reinforcement
a) The top as well as bottom reinforcement shall consist of at least two bars throughout the
member length
b) The tension steel ratio on any face at any section shall not be less than ρmin = 024 where fck
and fy are in MPa
The positive steel at a joint face must be at least equal to half the negative steel at that face
The steel provided at each of the top and bottom face of the member at any section along its
length shall be at least equal to one-fourth of the maximum negative moment steel provided
at the face of either joint It may be clarified that
redistribution of moments permitted in IS 456
1978 (clause 361) will be used only for vertical
load moments and not for lateral load moments
In an external joint both the top and the bottom
bars of the beam shall be provided with anchorage
length beyond the inner face of the column equal
to the development length in tension plus 10 times
the bar diameter minus the allowance for 90 degree
bend(s) (as shown in Fig 916) In an internal joint
both face bars of the beam shall be taken
continuously through the column
Fig 916 Anchorage of Beam Bars in an External Joint (IS 13920 1993)
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9112 अनदधयय सदढीकरण की सपलाइतसोग Splicing of longitudinal reinforcement
The longitudinal bars shall be spliced only if hoops are
provided over the entire splice length at a spacing not
exceeding 150 mm (as shown in Fig 917) The lap length
shall not be less than the bar development length in tension
Lap splices shall not be provided (a) within a joint (b)
within a distance of 2d from joint face and (c) within a
quarter length of the member where flexural yielding may
generally occur under the effect of earthquake forces Not
more than 50 percent of the bars shall be spliced at one
section
Use of welded splices and mechanical connections may also be made as per 25252 of
IS 456-1978 However not more than half the reinforcement shall be spliced at a section
where flexural yielding may take place
9113 वब सदढीकरण Web Reinforcement
Web reinforcement shall consist of vertical hoops A vertical hoop is a closed stirrup having a
135deg hook with a 10 diameter extension (but
not lt 75 mm) at each end that is embedded
in the confined core [as shown in (a) of
Fig 918] In compelling circumstances it
may also be made up of two pieces of
reinforcement a U-stirrup with a 135deg hook
and a 10 diameter extension (but not lt 75
mm) at each end embedded in the confined
core and a crosstie [as shown in (b) of Fig
918] A crosstie is a bar having a 135deg hook
with a 10 diameter extension (but not lt 75
mm) at each end The hooks shall engage
peripheral longitudinal bars
912 कॉलम तजनह आर सी इमारिो ो म भको प बलो ो का तवरोध करन क तलए िाला जािा ि Columns that are required to resist Earthquake Forces in RC Buildings
Columns the vertical members in RC buildings contain two types of steel reinforcement
namely
(a) long straight bars (called longitudinal bars) placed vertically along the length and
(b) closed loops of smaller diameter steel bars (called transverse ties) placed horizontally at
regular intervals along its full length
Fig 917 Lap Splice in Beam
(IS 13920 1993)
Fig 918 Beam Web Reinforcement (IS 13920 1993)
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Columns can sustain two types of damage namely axial-flexural (or combined compression-
bending) failure and shear failure Shear damage is brittle and must be avoided in columns by
providing transverse ties at close spacing
Closely spaced horizontal closed ties (Fig 919)
help in three ways namely
(i) they carry the horizontal shear forces
induced by earthquakes and thereby resist
diagonal shear cracks
(ii) they hold together the vertical bars and
prevent them from excessively bending
outwards(in technical terms this bending
phenomenon is called buckling) and
(iii) they contain the concrete in the column
within the closed loops The ends of the
ties must be bent as 135deg hooks Such hook
ends prevent opening of loops and
consequently bulging of concrete and
buckling of vertical bars
Construction drawings with clear details of closed ties are helpful in the effective implementation
at construction site In columns where the spacing between the corner bars exceeds 300mm the
Indian Standard prescribes additional links with 180deg hook ends for ties to be effective in holding
the concrete in its place and to prevent the buckling of vertical bars These links need to go
around both vertical bars and horizontal closed ties (Fig 920) special care is required to
implement this properly at site
Designing a column involves selection of
materials to be used (ie grades of concrete and
steel bars) choosing shape and size of the cross-
section and calculating amount and distribution
of steel reinforcement The first two aspects are
part of the overall design strategy of the whole
building The IS 13920 1993 requires columns
to be at least 300mm wide A column width of up
to 200 mm is allowed if unsupported length is less
than 4m and beam length is less than 5m
Columns that are required to resist earthquake
forces must be designed to prevent shear failure
by a skillful selection of reinforcement
Fig 919 Steel reinforcement in columns ndash closed ties
at close spacing improve the performance of column
under strong earthquake shaking
Fig 920 Extra links are required to keep the
concrete in place ndash 180deg links are necessary to
prevent the135deg tie from bulging outwards
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913 एकसीयल लोिि मबसय क तलए सामानय आवशयकिाएा General Requirements for Axial
Loaded Members
These requirements apply to frame members which have a factored axial stress in excess of
01 fck under the effect of earthquake forces
The minimum dimension of the member shall not be less than 200 mm However in frames
which have beams with centre to centre span exceeding 5 m or columns of unsupported
length exceeding 4 m the shortest dimension of the column shall not be less than 300 mm
The ratio of the shortest cross sectional dimension to the perpendicular dimension shall
preferably not be less than 04
9131 अनदधयय सदढीकरण Longitudinal Reinforcement
Lap splices shall be provided only in the central half
of the member length It should be proportioned as a
tension splice Hoops shall be provided over the
entire splice length at spacing not exceeding 150
mm centre to centre Not more than 50 percent of
the bars shall be spliced at one section
Any area of a column that extends more than 100
mm beyond the confined core due to architectural
requirements shall be detailed in the following
manner
a) In case the contribution of this area to strength
has been considered then it will have the minimum longitudinal and transverse
reinforcement as per IS 13920 1993
b) However if this area has been treated as non-structural the minimum reinforcement
requirements shall be governed by IS 456 1978 provisions minimum longitudinal and
transverse reinforcement as per IS 456 1978 (as shown in Fig 921)
9132 अनपरसथ सदढीकरण Transverse Reinforcement
Transverse reinforcement for circular columns shall consist of spiral or circular hoops In
rectangular columns rectangular hoops may be used A rectangular hoop is a closed stirrup
having a 135deg hook with a 10 diameter extension (but not lt 75 mm) at each end that is
embedded in the confined core [as shown in (A) of Fig 922]
Fig 921 Reinforcement requirement for Column with more than 100 mm projection beyond core(IS 13920 1993)
Fig 922 Transverse Reinforcement in Column (IS 13920 1993)
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The parallel legs of rectangular hoop shall be spaced not more than 300 mm centre to centre
If the length of any side of the hoop exceeds 300 mm a crosstie shall be provided [as shown
in (B) of Fig 922] Alternatively a pair of overlapping hoops may be provided within the
column [as shown in (C) of Fig 922] The hooks shall engage peripheral longitudinal bars
The spacing of hoops shall not exceed half the least lateral dimension of the column except
where special confining reinforcement is provided as per Para 915 below
914 बीम-कॉलम जोड़ जो आर सी भवनो ो म भको प बलो ो का तवरोध करि ि Beam-Column Joints
that resist Earthquakes Forces in RC Buildings
In RC buildings portions of columns that are
common to beams at their intersections are
called beam column joints (Fig 923) The
joints have limited force carrying capacity
When forces larger than these are applied
during earthquakes joints are severely
damaged Repairing damaged joints is
difficult and so damage must be avoided
Thus beam-column joints must be designed
to resist earthquake effects
Under earthquake shaking the beams adjoining a joint are subjected to moments in the same
(clockwise or counter-clockwise) direction
Under these moments the top bars in the
beam-column joint are pulled in one
direction and the bottom ones in the
opposite direction These forces are
balanced by bond stress developed between
concrete and steel in the joint region
(Fig 924)
If the column is not wide enough or if the
strength of concrete in the joint is low there
is insufficient grip of concrete on the steel
bars In such circumstances the bar slips
inside the joint region and beams loose
their capacity to carry load Further under
the action of the above pull-push forces at top and bottom ends joints undergo geometric
distortion one diagonal length of the joint elongates and the other compresses
If the column cross-sectional size is insufficient the concrete in the joint develops diagonal
cracks
Fig 923 Beam-Column Joints are critical parts of a
building ndash they need to be designed
Fig924 Pull-push forces on joints cause two
problems ndash these result in irreparable damage in joints
under strong seismic shaking
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9141 बीम-कॉलम जोड़ मजबि करन क तलए सामानय आवशयकिाएा General Requirements
for Reinforcing the Beam-Column Joint
Diagonal cracking and crushing of concrete in joint
region should be prevented to ensure good
earthquake performance of RC frame buildings
(Fig 925)
Using large column sizes is the most effective
way of achieving this
In addition closely spaced closed-loop steel ties
are required around column bars to hold
together concrete in joint region and to resist
shear forces
Intermediate column bars also are effective in
confining the joint concrete and resisting
horizontal shear forces Providing closed-loop
ties in the joint requires some extra effort
IS 13920ndash1993 recommends continuing the
transverse loops around the column bars
through the joint region
In practice this is achieved by preparing the cage of
the reinforcement (both longitudinal bars and
stirrups) of all beams at a floor level to be prepared
on top of the beam formwork of that level and
lowered into the cage (Fig 926)
However this may not always be possible
particularly when the beams are long and the entire
reinforcement cage becomes heavy
The gripping of beam bars in the joint region is
improved first by using columns of reasonably
large cross-sectional size
The Indian Standard IS 13920-1993 requires building columns in seismic zones III IV and V to
be at least 300mm wide in each direction of the cross-section when they support beams that are
longer than 5m or when these columns are taller than 4m between floors (or beams)
In exterior joints where beams terminate at columns longitudinal beam bars need to be anchored
into the column to ensure proper gripping of bar in joint The length of anchorage for a bar of
grade Fe415 (characteristic tensile strength of 415MPa) is about 50 times its diameter This
Fig 925 Closed loop steel ties in beam-column
joints ndash such ties with 135deg hooks resist the ill
effects of distortion of joints
Fig 926 Providing horizontal ties in the joints ndash
three-stage procedure is required
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length is measured from the face of the column to the end of the bar anchored in the column
(Fig 927)
In columns of small widths and when beam
bars are of large diameter (Fig 928(a)) a
portion of beam top bar is embedded in the
column that is cast up to the soffit of the
beam and a part of it overhangs It is difficult
to hold such an overhanging beam top bar in
position while casting the column up to the
soffit of the beam Moreover the vertical
distance beyond the 90ordm bend in beam bars is
not very effective in providing anchorage
On the other hand if column width is large
beam bars may not extend below soffit of the
beam (Fig 928 (b)) Thus it is preferable to
have columns with sufficient width
In interior joints the beam bars (both top and
bottom) need to go through the joint without
any cut in the joint region Also these bars
must be placed within the column bars and
with no bends
915 तवशष सीतमि सदढीकरण Special Confining Reinforcement
This requirement shall be met with unless a
larger amount of transverse reinforcement is
required from shear strength considerations
Special confining reinforcement shall be
provided over a length lsquolorsquo from each
joint face towards mid span and on
either side of any section where flexural
yielding may occur under the effect of
earthquake forces (as shown in Fig 929)
The length lsquolorsquo shall not be less than
(a) larger lateral dimension of the
member at the section where yielding
occurs
(b) 16 of clear span of the member and
(c) 450 mm
Fig 929 Column and Joint Detailing (IS 13920 1993)
Fig 927 Anchorage of beam bars in exterior
joints ndash diagrams show elevation of joint region
Fig 928 Anchorage of beam bars in interior
jointsndash diagrams (a) and (b) show cross-sectional
views in plan of joint region
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When a column terminates into a footing or mat special confining reinforcement shall extend
at least 300 mm into the footing or mat (as shown in Fig 930)
When the calculated point of contra-flexure
under the effect of gravity and earthquake
loads is not within the middle half of the
member clear height special confining
reinforcement shall be provided over the full
height of the column
Columns supporting reactions from discontinued stiff members such as walls shall be
provided with special confining reinforcement over their full height (as shown in Fig 931)
This reinforcement shall also be placed above the discontinuity for at least the development
length of the largest longitudinal bar in the column Where the column is supported on a wall
this reinforcement shall be provided
over the full height of the column it
shall also be provided below the
discontinuity for the same development
length
Special confining reinforcement shall
be provided over the full height of a
column which has significant variation
in stiffness along its height This
variation in stiffness may result due to
the presence of bracing a mezzanine
floor or a RCC wall on either side of
the column that extends only over a part
of the column height (as shown in Fig
931)
916 तवशषिः भको पीय कषतर म किरनी दीवारो ो वाली इमारिो ो का तनमायण Construction of Buildings
with Shear Walls preferably in Seismic Regions
Reinforced concrete (RC) buildings often have vertical
plate-like RC walls called Shear Walls in addition to
slabs beams and columns These walls generally start
at foundation level and are continuous throughout the
building height Their thickness can be as low as
150mm or as high as 400mm in high rise buildings
Shear walls are usually provided along both length and
width of buildings Shear walls are like vertically-
oriented wide beams that carry earthquake loads
downwards to the foundation (Fig 932)
Fig 932 Reinforced concrete shear walls in
buildings ndash an excellent structural system for
earthquake resistance
Fig 930 Provision of Special confining reinforcement in Footings (IS 13920 1993)
Fig 931 Special Confining Reinforcement Requirement for
Columns under Discontinued Walls (IS 13920 1993)
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Properly designed and detailed buildings with shear walls have shown very good performance in
past earthquakes Shear walls in high seismic regions require special detailing Shear walls are
efficient both in terms of construction cost and effectiveness in minimizing earthquake damage
in structural and non-structural elements (like glass windows and building contents)
Shear walls provide large strength and
stiffness to buildings in the direction of their
orientation which significantly reduces lateral
sway of the building and thereby reduces
damage to structure and its contents
Since shear walls carry large horizontal
earthquake forces the overturning effects on
them are large Thus design of their
foundations requires special attention
Shear walls should be provided along
preferably both length and width However if
they are provided along only one direction a
proper grid of beams and columns in the
vertical plane (called a moment-resistant
frame) must be provided along the other
direction to resist strong earthquake effects
Door or window openings can be provided in shear walls but their size must be small to
ensure least interruption to force flow through walls
Shear walls in buildings must be symmetrically located in plan to reduce ill-effects of twist in
buildings (Fig 933)
Shear walls are more effective when located along exterior perimeter of the building ndash such a
layout increases resistance of the building to twisting
9161 िनय तिजाइन और किरनी दीवारो ो की जयातमति Ductile Design and Geometry of Shear
Walls
Shear walls are oblong in cross-section ie one dimension of the cross-section is much larger
than the other While rectangular cross-section is common L- and U-shaped sections are also
used Overall geometric proportions of the wall types and amount of reinforcement and
connection with remaining elements in the building help in improving the ductility of walls The
Indian Standard Ductile Detailing Code for RC members (IS13920-1993) provides special
design guidelines for ductile detailing of shear walls
917 इमपरवड़ तिजाइन रणनीतियाो Improved design strategies
9171 िातनकारक भको प परभाव स भवनो ो का सोरकषण Protection of Buildings from Damaging
Earthquake Effects
Conventional seismic design attempts to make buildings that do not collapse under strong
earthquake shaking but may sustain damage to non-structural elements (like glass facades) and
to some structural members in the building There are two basic technologies ndashBase Isolation
Fig 933 Shear walls must be symmetric in plan
layout ndash twist in buildings can be avoided
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Devices and Seismic Dampers which are used to protect buildings from damaging earthquake
effects
9172 आधार अलगाव Base Isolation
The idea behind base isolation is to detach (isolate) the building from the ground in such a way
that earthquake motions are not transmitted up through the building or at least greatly reduced
As illustrated in Fig 934 when the ground shakes the rollers freely roll but the building
above does not move Thus no force is
transferred to the building due to shaking of
the ground simply the building does not
experience the earthquake
As illustrated in Fig 935 if the same
building is rested on flexible pads that offer
resistance against lateral movements then
some effect of the ground shaking will be
transferred to the building above
As illustrated in Fig 936 if the flexible
pads are properly chosen the forces induced
by ground shaking can be a few times
smaller than that experienced by the
building built directly on ground namely a
fixed base building
9173 भको पी सोज Seismic Dampers
Seismic dampers are special devices introduced in the building to absorb the energy provided by
the ground motion to the building These dampers act like the hydraulic shock absorbers in cars ndash
much of the sudden jerks are absorbed in the hydraulic fluids and only little is transmitted above
to the chassis of the car
When seismic energy is transmitted through them dampers absorb part of it and thus damp the
motion of the building Commonly used types of seismic dampers (Fig 937) include
Fig 934 Hypothetical Building
Fig 935 Base Isolated Building
Fig 936 Fixed-Base Building
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Viscous dampers ndash Energy is absorbed by
silicone-based fluid passing between piston-
cylinder arrangement
Friction dampers ndash Energy is absorbed by
surfaces with friction between them rubbing
against each other
Yielding dampers ndash Energy is absorbed by
metallic components that yield
In India friction dampers have been provided in an
18-storey RC frame structure in Gurgaon
918 तिजाइन उदािरण Design Example ndash Beam Design of RC Frame with Ductile
Detailing
Exercise ndash 2 Beam Design of RC Frame Building as per Provision of IS 13920 1993 and IS
1893 (Part 1) 2002 Beam marked ABC is considered for Design
Fig 937 Seismic Energy Dissipation Devices
each device is suitable for a certain building
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79
ELEVATION
Solution
1 General Data Grade of Concrete = M 25
Grade of steel = Fe 415 Tor Steel
2 Load Combinations
As per Cl 63 of IS 1893 (Part 1) 2002 following are load combinations for Earthquake
Loading
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S No Load Combination DL LL EQ Remark
1 15 DL + 15 LL 15 15 ndash As per Table ndash 8
of IS 1893 (Part
1) 2002 2 12 (DL + LL
+ EQx) 15 025 or 050 +12
3 12 (DL + LL ndash EQx) 15 025 or 050 ndash12
4 12 (DL + LL + EQy) 15 025 or 050 +12
5 12 (DL + LL ndash EQy) 15 025 or 050 ndash12
6 15 (DL + EQx) 15 +15
7 15 (DL ndash EQx) 15 ndash15
8 15 (DL + EQy) 15 +15
9 15 (DL ndash EQy) 15 ndash15
10 09 DL + 15 EQx 15 +15
11 09 DL ndash 15 EQx 15 ndash15
12 09 DL + 15 EQy 15 +15
13 09 DL ndash 15 EQy 15 ndash15
EQx implies EQ Loading in X ndash direction amp EQy implies EQ Loading in Y ndash direction
where X amp Y are orthogonal directions and Z is vertical direction These load combinations
are for EQ Loading In practice Wind Load should also be considered in lieu of EQ Load
and critical of the two should be used in the design
In this exercise emphasis is to show calculations for ductile design amp detailing of building
elements subjected to Earthquake in the plan considered Beams parallel to Y ndash direction are
not significantly affected by Earthquake force in X ndash direction (except in case of highly
unsymmetrical building) and vice versa Beams parallel to Y ndash direction are designed for
Earthquake loading in Y ndash direction only
Torsion effect is not considered in this example
3 Force Data
For Beam AB force resultants for various load cases (ie DL LL amp EQ Load) from
Computer Analysis (or manually by any method of analysis) to illustrate the procedure of
design are tabulated below
Table ndash A Force resultants in beam AB for various load cases
Load Case Left End Centre Right End
Shear
(KN)
Moment
(KN-m)
Shear
(KN)
Moment
(KN-m)
Shear
(KN)
Moment
(KN-m)
DL ndash 51 ndash 37 4 32 59 ndash 56
LL ndash 14 ndash 12 1 11 16 ndash 16
EQY 79 209 79 11 79 ndash 119
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Table ndash B Force resultants in beam AB for different load combinations
Load Combinations Left End Centre Right End
Shear
(KN)
Moment
(KN-m)
Shear
(KN)
Moment
(KN-m)
Shear
(KN)
Moment
(KN-m)
15 DL + 15 LL 98 ndash 74 7 64 111 ndash 108
12 (DL + LL + EQy) 31 205 101 52 172 ndash 303
12 (DL + LL ndash EQy) 162 ndash 300 92 31 22 159
15 (DL + EQy) 44 261 127 61 209 ndash 372
15 (DL ndash EQy) 97 ndash 371 115 34 33 205
09 DL + 15 EQy 75 283 124 42 174 ndash 339
09 DL ndash 15 EQy 167 ndash 349 117 15 68 238
4 Various checks for Flexure Member
(i) Check for Axial Stress
As per Cl 611 of IS 13920 1993 flexural axial stress on the member under EQ loading
shall not exceed 01 fck
Factored Axial Force = 000 KN
Factored Axial Stress = 000 MPa lt 010 fck OK
Hence the member is to be designed as Flexure Member
(ii) Check for Member size
As per Cl 613 of IS 13920 1993 width of the member shall not be less than 200 mm
Width of the Beam B = 250 mm gt 200 mm OK
Depth of Beam D = 550 mm
As per Cl 612 member shall have a width to depth ratio of more than 03
BD = 250550 = 04545 gt 03 OK
As per Cl 614 depth of member shall preferably be not more than 14 of the clear span
ie (DL) lt 14 or (LD) gt4
Span = 4 m LD = 4000550 = 727 gt 4 OK
Check for Limiting Longitudinal Reinforcement
Nominal cover to meet Durability requirements as per = 30 mm
Table ndash 16 of IS 4562000 (Cl 2642) for Moderate Exposure
Effective depth for Moderate Exposure conditions = 550 ndash 30 ndash 20 ndash (202)
with 20 mm of bars in two layers = 490 mm
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As per Cl 621 (b) of IS 13920 1993 tension steel ratio on any face at any section shall not
be less than = (024 radic fck) fy
= (024 radic25) 415 = 0289 asymp 029
Min Reinforcement = (029100) X 250 X 490 = 356 mm2
Max Reinforcement 25 = (25100) X 250 X 490 = 3063 mm2
(iii) Design for Flexure
Design for Hogging Moment at support A
At end A from Table ndash B Mu = 371 KN-m
Therefore Mu bd2 = 371x10
6 (250 x 490 x 490) = 618
Referring to Table ndash 51 of SP ndash 16 for drsquod = 55490 = 011
We get Ast at top = 2013 Asc = 0866
Therefore Ast at top = (2013100) x 250 x 490
= 2466 mm2
gt 356 mm2 (Min Reinforcement)
lt 3063 mm2 (Max Reinforcement)
Asc at bottom = 0866
As per Cl 623 of IS 13290 1993 positive steel at a joint face must be at least equal to half
the ndashve steel at that face Therefore Asc at bottom must be at least 50 of Ast hence
Revised Asc = 20132 = 10065
Asc at bottom = (10065100) x 250 x 490
= 1233 mm2 gt 426 mm
2 (Min Reinforcement)
lt 3063 mm2 (Max Reinforcement)
Design for Sagging Moment at support A
Mu = 283 KN-m
The beam will be designed as T-beam The limiting capacity of the T-beam assuming xu lt Df
and xu lt xumax may be calculated as follows
Mu = 087 fy Ast d [1- (Ast fy bf d fck)] -------- (Eq ndash 1)
Where Df = Depth of Flange
= 150 mm
xu = Depth of Neutral Axis
xumax = Limiting value of Neutral Axis
= 048 d
= 048 X 490
= 23520 mm
bw = 250 mm
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bf = Width of Flange
= (L06) + bw + 6 Df or cc of beam
= (07 X 40006) + 250 + 6 X 150
= 467 + 250 + 900 = 1617 mm or 4000 mm cc
[Lower of two is to be adopted]
Substituting the values in Eq ndash 1 and solving the quadratic equation
283 X 106 = 087 X 415 Ast X 490 [1ndash (Ast X 415) (1617 X 490 X 25)]
= 1769145 Ast [1 ndash 2095 X 10-5
Ast]
283 X 106 = 1769145 Ast ndash 3706 Ast
2]
3706 Ast2 ndash 1769145 Ast + 283 X 10
6 = 0
Ast = [1769145 plusmn radic(17691452 ndash 4 X 3706 X 283 X 10
6)] 2 X 3706
= [1769145 plusmn radic(3129874 X 1010
ndash 4195192 X 106)] 2 X 3706
= (1769145 plusmn 16463155) 7412
Ast at bottom = 165717 mm2 gt 35600 mm
2
lt 306300 mm2 OK
It is necessary to check the design assumptions before finalizing the reinforcement
xu = (087 fy Ast) (036 fck bf)
= (087 X 415 X 1657) (036 X 25 X 1617)
= 4110 mm lt 150 mm OK
lt df
lt xumax = 048 X 490 = 235 mm OK
Ast = [1657(250X490)] X 100 = 1353
As per Cl 624 ldquoSteel provided at each of the top amp bottom face of the member at any one
section along its length shall be at least equal to 14th
of the maximum (-ve) moment steel
provided at the face of either joint
For Centre Mu = 64 KN-m
64 X 106 = 087 X 415 Ast X 490 [1ndash (Ast X 415) (1617 X 490 X 25)]
= 1769145 Ast [1 ndash 2095 X 10-5
Ast]
64 X 106 = 1769145 Ast ndash 3706 Ast
2]
3706 Ast2 ndash 1769145 Ast + 64 X 10
6 = 0
Ast = [1769145 plusmn radic(17691452 ndash 4 X 3706 X 64 X 10
6)] 2 X 3706
= 365 mm2
For Right Support Mu = 238 KN-m
238 X 106 = 087 X 415 Ast X 490 [1ndash (Ast X 415) (1617 X 490 X 25)]
= 1769145 Ast [1 ndash 2095 X 10-5
Ast]
238 X 106 = 1769145 Ast ndash 3706 Ast
2]
3706 Ast2 ndash 1769145 Ast + 238 X 10
6 = 0
Ast = [1769145 plusmn radic(17691452 ndash 4 X 3706 X 238 X 10
6)] 2 X 3706
= 1386 mm2
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84
(iv) Reinforcement Requirement
Top reinforcement is larger of Ast at top for hogging moment or Asc at top for sagging
moment ie 2466 mm2 or 968 mm
2 Hence provide 2466 mm
2 at top
Bottom reinforcement is larger of Asc at bottom for hogging moment or Ast at bottom for
sagging moment ie 1233 mm2 or 1936 mm
2 Hence provide 1936 mm
2 at bottom
Details of Reinforcement
Top Reinforcement
Beam AB Left End Centre Right End
Hogging Moment ndash 371 - ndash 371
Mu bd2 618 - 618
Ast at top 2013 - 2013
Asc at bottom 0866 lt 2013 2 =
10065 Hence
revised Asc = 10065
- 0866
Revised to
10065 as per Cl
623 of IS
139201993
Bottom Reinforcement
Sagging Moment 283 64 238
Ast at bottom Ast req = 1657 mm2
= 1353
gt 20132 =
10065 OK
Provide Ast at bottom
= 1353
Ast req = 365 mm2
= 0298
gt 029
gt 20134 =
0504 OK
As per Cl 624 of IS
139201993
Provide Ast at bottom
= 0504
Ast req = 1386 mm2
= 117
gt 029
gt 20132 =
10065
Provide Ast at
bottom = 117
Asc at top Asc req = 1657 2
= 829 mm2
= 0677
gt 029
gt 2013 4 =
0504 OK
Asc req = 05042
= 0252
gt 029 Provide MinAsc = 029
Asc req = 1657 2
= 829 mm2
= 0677
gt 029
gt 2013 4
= 0504
OK
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Summary of Reinforcement required
Beam Left End Centre Right End
Top = 2013
= 2466 mm2
Bottom = 1353
= 1658 mm2
Top = 0504
= 618 mm2
Bottom = 0504
= 618 mm2
Top = 2013
= 2466 mm2
Bottom = 10065
= 1233 mm2
Reinforcement provided
2 ndash 20Φ cont + 4 ndash 25Φ extra
Ast = 2592 mm2 (2116)
2 ndash 20Φ cont + 2 ndash 20Φ extra
+ 2 ndash 16 Φ
Ast = 1658 mm2 (1353)
2 ndash 20Φ cont
Ast = 628 mm2 (0512)
2 ndash 20Φ cont
Ast = 628 mm2 (0512)
2 ndash 20Φ cont
+ 4 ndash 25Φ extra
Top = 2592 mm2
2 ndash 20Φ cont
+ 2 ndash 20Φ extra + 2 ndash 16Φ
Ast = 1658 mm2 (1353)
Details of Reinforcement
Ld = Development Length in tension
db = Dia of bar
For Fe 415 steel and M25 grade concrete as per Table ndash 65 of SP ndash 16
For 25Φ bars 1007 + 10Φ - 8Φ = 1007+50 = 1057 mm
For 20Φ bars 806 + 2Φ = 806+40 = 846 mm
(v) Design for Shear
Tensile steel provided at Left End = 2116
Permissible Design Stress of Concrete
(As per Table ndash 19 of IS 4562000) τc = 0835 MPa
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Design Shear Strength of Concrete = τc b d
= (0835 X 250 X 490) 1000
= 102 KN
Similarly Design Shear Strength of Concrete at centre for Ast = 0512
τc = 0493 MPa
Shear Strength of Concrete at centre = τc b d
= (0493 X 250 X 490) 1000
= 6040 KN
(vi) Shear force due to Plastic Hinge Formation at the ends of the beam
The additional shear due to formation of plastic hinges at both ends of the beams is evaluated
as per Cl 633 of IS 139201993 is given by
Vsway to right = plusmn 14 [MulimAs
+ MulimBh
] L
Vsway to left = plusmn 14 [MulimAh
+ MulimBs
] L
Where
MulimAs
= Sagging Ultimate Moment of Resistance of Beam Section at End A
MulimAh
= Hogging Ultimate Moment of Resistance of Beam Section at End A
MulimBh
= Sagging Ultimate Moment of Resistance of Beam Section at End B
MulimBs
= Hogging Ultimate Moment of Resistance of Beam Section at End B
At Ends beam is provided with steel ndash pt = 2116 pc = 1058
Referring Table 51 of SP ndash 16 for pt = 2116 pc = 1058
The lowest value of MuAh
bd2 is found
MuAh
bd2 = 645
Hogging Moment Capacity at End A
MuAh
= 645 X 250 X 4902
= 38716 X 108 N-mm
= 38716 KN-m
Similarly for MuAs
pt = 1058 pc = 2116
Contribution of Compressive steel is ignored while calculating the Sagging Moment
Capacity at T-beam
MuAs
= 087 fy Ast d [1- (Ast fy bf d fck)]
= 087 X 415 X 1658 X 490 [1ndash (1658 X 415 1617 X 490 X 25)]
= 28313 KN-m
Similarly for Right End of beam
MuBh
= 38716 KN-m amp MuBs
= 28313 KN-m
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Shear due to Plastic Hinge is calculated as
Vsway to right = plusmn 14 [MuAs
+ MuBh
] L
= plusmn 14 [28313 + 38716] 4
= 23460 KN
Vsway to left = plusmn 14 [MuAh
+ MuBs
] L
= plusmn 14 [38716 + 28313] 4
= 23460 KN
Design Shear
Dead Load of Slab = 50 KNm2 Live Load = 40 KNm
2
Load due to Slab in Beam AB = 2 X [12 X 4 X 2] X 5 = 40 KN (10 KNm)
Self Wt Of Beam = 025 X 055 X 25 X 4 = 1375 KN (344 KNm)
asymp 1400 KN
Live Load = 2 X [12 X 4 X 2] X 4 = 32 KN (8 KNm)
Shear Force due to DL = 12 X [40 + 14] = 27 KN
Shear Force due to LL = 12 X [32] = 16 KN
As per Cl 633 of IS 139201993 the Design shear at End A ie Vua and Design Shear at
End B ie Vub are computed as
(i) For Sway Right
Vua = VaD+L
ndash 14 [MulimAs
+ MulimBh
] LAB
Vub = VbD+L
+ 14 [MulimAs
+ MulimBh
] LAB
(ii) For Sway Left
Vua = VaD+L
+ 14 [MulimAh
+ MulimBs
] LAB
Vub = VbD+L
ndash 14 [MulimAh
+ MulimBs
] LAB
Where
VaD+L
amp VbD+L
= Shear at ends A amp B respectively due to vertical load with
Partial Safety Factor of 12 on Loads
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VaD+L
= VbD+L
= 12 (D+L) 2
--------------For equ (i)
---------------For equ (ii)
14 X [MuAs
+ MuBh
] L = 23460 KN
14 X [MuAh
+ MuBs
] L = 23460 KN
VaD = Vb
D = 12 X 27 = 324
= 516
VaL = Vb
L = 12 X 16 = 192
Vua = [12 (27+16)] ndash 23460 = 516 ndash 23460 = (-) 18300 KN
Vub = [12 (27+16)] + 23460 = 516 + 23460 = (+) 28620 KN
Vub = [12 (27+16)] + 23460 = 516 + 23460 = (+) 28620 KN
Vua = [12 (27+16)] ndash 23460 = 516 ndash 23460 = (-) 18300 KN
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As per Cl 633 of IS 139201993 the Design Shear Force to be resisted shall be of
maximum of
(i) Calculate factored SF as per analysis ( Refer Table ndash B)
(ii) Shear Force due to formation of Plastic Hinges at both ends of the beam plus
factored gravity load on the span
Hence Design shear Force Vu will be 28620 KN (corresponding to formation of Plastic
Hinge)
From Analysis as per Table ndash B SF at mid-span of the beam is 127 KN However Shear
due to formation of Plastic Hinge is 23460 KN Hence design shear at centre of span is
taken as 23460 KN
The required capacity of shear reinforcement at ends
Vus = Vu - Vc
= 28620 ndash 102
= 18420 KN
And at centre Vus = 23460 ndash 6040
= 17420 KN
At supports
Vus d = 28620 49 = 584 KNcm
Therefore requirement of stirrups is
12Φ ndash 2 legged strippus 135 cc [Vus d = 606]
However provide 12Φ ndash 2 legged strippus 120 cc as per provision of Cl 635 of IS
139201993 [Vus d = 6806]
At centre
Vus d = 23460 49 = 478 KNcm
Provide 12Φ ndash 2 legged strippus 170 cc [Vus d = 4804]
As per Cl 635 of IS 139201993 the spacing of stirrups in the mid-span should not
exceed d2 = 4902 = 245 mm
Minimum Shear Reinforcement as per Cl 26516 of IS 4562000 is
Sv = Asv X 08 fy 046
= (2 X 79 X 087 X 415) (250 X 04)
= 570 mm
As per CL 635 of IS 139201993 ldquoSpacing of Links over a length of 2d at either end of
beam shall not exceed
(i) d4 = 4904 = 12250 mm
(ii) 8 times dia of smallest longitudinal bar = 8 X 16 = 128 mm
However it need not be less than 100 mm
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The reinforcement detailing is shown as below
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अधयाय Chapter ndash 10
अलप सामरथय तचनाई सोरचनाओो क तनमायण Construction of Low Strength Masonry Structures
Two types of construction are included herein namely
a) Brick construction using weak mortar and
b) Random rubble and half-dressed stone masonry construction using different mortars such as
clay mud lime-sand and cement sand
101 भको प क दौरान ईोट तचनाई की दीवारो ो का वयविार Behaviour of Brick Masonry Walls
during Earthquakes
Of the three components of a masonry building (roof wall and foundation as illustrated in
Fig101) the walls are most vulnerable to damage caused by horizontal forces due to earthquake
Ground vibrations during earthquakes cause inertia forces at locations of mass in the building (Fig 102) These forces travel through the roof and walls to the foundation The main emphasis
is on ensuring that these forces reach the ground without causing major damage or collapse
A wall topples down easily if pushed
horizontally at the top in a direction
perpendicular to its plane (termed weak
Fig 101 Basic components of Masonry Building
Fig 103 For the direction of Earthquake shaking
shown wall B tends to fail
at its base
Fig 102 Effect of Inertia in a building when shaken
at its base
Fig 104 Direction of force on a wall critically determines
its earthquake performance
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direction) but offers much greater resistance if pushed along its length (termed strong direction) (Fig 103 amp 104)
The ground shakes simultaneously in the vertical and two horizontal directions during
earthquakes However the horizontal vibrations are the most damaging to normal masonry
buildings Horizontal inertia force developed at the
roof transfers to the walls acting either in the weak
or in the strong direction If all the walls are not tied
together like a box the walls loaded in their weak
direction tend to topple
To ensure good seismic performance all walls must
be joined properly to the adjacent walls In this way
walls loaded in their weak direction can take
advantage of the good lateral resistance offered by
walls loaded in their strong direction (Fig 105)
Further walls also need to be tied to the roof and
foundation to preserve their overall integrity
102 तचनाई वाली इमारिो ो म बॉकस एकशन कस सतनतिि कर How to ensure Box Action in
Masonry Buildings
A simple way of making these walls behave well during earthquake shaking is by making them
act together as a box along with the roof at the top and with the foundation at the bottom A
number of construction aspects are required to ensure this box action
Firstly connections between the walls should be good This can be achieved by (a) ensuring
good interlocking of the masonry courses at the junctions and (b) employing horizontal bands
at various levels particularly at the lintel level
Secondly the sizes of door and window
openings need to be kept small The smaller
the opening the larger is the resistance
offered by the wall
Thirdly the tendency of a wall to topple
when pushed in the weak direction can be
reduced by limiting its length-to-thickness
and height to-thickness ratios Design codes
specify limits for these ratios A wall that is
too tall or too long in comparison to its
thickness is particularly vulnerable to
shaking in its weak direction (Fig 106)
Fig 106 Slender walls are vulnerable
Fig 105 Wall B properly connected to Wall A
(Note roof is not shown) Walls A
(loaded in strong direction) support
Walls B (loaded in weak direction)
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Brick masonry buildings have large mass and hence attract large horizontal forces during
earthquake shaking They develop numerous cracks under both compressive and tensile forces
caused by earthquake shaking The focus of earthquake resistant masonry building construction
is to ensure that these effects are sustained without major damage or collapse Appropriate choice
of structural configuration can help achieve this
The structural configuration of masonry buildings
includes aspects like (a) overall shape and size of the
building and (b) distribution of mass and
(horizontal) lateral load resisting elements across the
building
Large tall long and un-symmetric buildings perform
poorly during earthquakes A strategy used in making
them earthquake resistant is developing good box
action between all the elements of the building ie
between roof walls and foundation (Fig 107) For
example a horizontal band introduced at the lintel
level ties the walls together and helps to make them
behave as a single unit
103 कषतिज बि की भतमका Role of Horizontal Bands
Horizontal bands are the most important
earthquake-resistant feature in masonry
buildings The bands are provided to hold a
masonry building as a single unit by tying all
the walls together and are similar to a closed
belt provided around cardboard boxes
(Fig 108 amp 109)
The lintel band undergoes bending and pulling actions during earthquake shaking
(Fig1010)
To resist these actions the construction of lintel band requires special attention
Fig 107 Essential requirements to ensure
box action in a masonry building
Fig 108 Building with flat roof
Fig 109 Two-storey Building with pitched roof
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Bands can be made of wood (including bamboo splits) or of reinforced concrete (RC) the
RC bands are the best (Fig 1011)
The straight lengths of the band must be properly connected at the wall corners
In wooden bands proper nailing of straight lengths with spacers is important
In RC bands adequate anchoring of steel links with steel bars is necessary
The lintel band is the most important of all and needs to be provided in almost all buildings
The gable band is employed only in buildings with pitched or sloped roofs
In buildings with flat reinforced concrete or reinforced brick roofs the roof band is not
required because the roof slab also plays the role of a band However in buildings with flat
timber or CGI sheet roof roof band needs to be provided In buildings with pitched or sloped
roof the roof band is very important
Plinth bands are primarily used when there is concern about uneven settlement of foundation
soil
Lintel band Lintel band is a band provided at lintel level on all load bearing internal external
longitudinal and cross walls
Roof band Roof band is a band provided immediately below the roof or floors Such a band
need not be provided underneath reinforced concrete or brick-work slabs resting on bearing
Fig 1010 Bending and pulling in lintel bands ndash Bands must be capable of resisting these actions
Fig 1011 Horizontal Bands in masonry buildings ndash RC bands are the best
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walls provided that the slabs are continuous over the intermediate wall up to the crumple
sections if any and cover the width of end walls fully or at least 34 of the wall thickness
Gable band Gable band is a band provided at the top of gable masonry below the purlins This
band shall be made continuous with the roof band at the eaves level
Plinth band Plinth band is a band provided at plinth level of walls on top of the foundation
wall This is to be provided where strip footings of masonry (other than reinforced concrete or
reinforced masonry) are used and the soil is either soft or uneven in its properties as frequently
happens in hill tracts This band will serve as damp proof course as well
104 अधोलोब सदढीकरण Vertical Reinforcement
Vertical steel at corners and junctions of walls which are up to 340 mm (1frac12 brick) thick shall be
provided as specified in Table 101 For walls thicker than 340 mm the area of the bars shall be
proportionately increased
No vertical steel need be provided in category A building The vertical reinforcement shall be
properly embedded in the plinth masonry of foundations and roof slab or roof band so as to
develop its tensile strength in bond It shall be passing through the lintel bands and floor slabs or
floor level bands in all storeys
Table ndash 101 Vertical Steel Reinforcement in Masonry Walls with Rectangular Masonry Units (IS 4326 1993)
No of Storeys Storey Diameter of HSD Single Bar in mm at Each Critical Section
Category B Category C Category D Category E One mdash Nil Nil 10 12
Two Top
Bottom
Nil
Nil
Nil
Nil
10
12
12
16
Three Top
Middle
Bottom
Nil
Nil
Nil
10
10
12
10
12
12
12
16
16
Four Top
Third
Second
Bottom
10
10
10
12
10
10
12
12
10
12
16
20
Four storeyed
building not
permitted
NOTES
1 The diameters given above are for HSD bars For mild-steel plain bars use equivalent diameters as given under
Table ndash 106 Note 2
2 The vertical bars will be covered with concrete M15 or mortar 1 3 grade in suitably created pockets around the
bars This will ensure their safety from corrosion and good bond with masonry
3 In case of floorsroofs with small precast components also refer 923 of IS 4326 1993 for floorroof band details
Bars in different storeys may be welded (IS 2751 1979 and IS 9417 1989 as relevant) or
suitably lapped
Vertical reinforcement at jambs of window and door openings shall be provided as per
Table ndash 101 It may start from foundation of floor and terminate in lintel band (Fig 1017)
Typical details of providing vertical steel in brickwork masonry with rectangular solid units
at corners and T-junctions are shown in Fig 1012
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105 दीवारो ो म सराखो ो का सोरकषण Protection of Openings in Walls
Horizontal bands including plinth band lintel band and roof band are provided in masonry
buildings to improve their earthquake performance Even if horizontal bands are provided
masonry buildings are weakened by the openings in their walls
Embedding vertical reinforcement bars in the edges of the wall piers and anchoring them in the
foundation at the bottom and in the roof band at the top forces the slender masonry piers to
undergo bending instead of rocking In wider wall piers the vertical bars enhance their capability
to resist horizontal earthquake forces and delay the X-cracking Adequate cross-sectional area of
these vertical bars prevents the bar from yielding in tension Further the vertical bars also help
protect the wall from sliding as well as from collapsing in the weak direction
However the most common damage observed after an earthquake is diagonal X-cracking of
wall piers and also inclined cracks at the corners of door and window openings
When a wall with an opening deforms during earthquake shaking the shape of the opening
distorts and becomes more like a rhombus - two opposite corners move away and the other two
come closer Under this type of deformation the corners that come closer develop cracks The
cracks are bigger when the opening sizes are larger Steel bars provided in the wall masonry all
Fig 1012 Typical Details of Providing Vertical Steel Bars in Brick Masonry (IS 4326 1993)
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around the openings restrict these cracks at the corners In summary lintel and sill bands above
and below openings and vertical reinforcement adjacent to vertical edges provide protection
against this type of damage (Fig 1013)
106 भको प परतिरोधी ईोट तचनाई भवन क तनमायण िि सामानय तसदाोि General Principles for
Construction of Earthquake Resistant Brick Masonry Building
Low Strength Masonry constructions should not be permitted for important buildings
It will be useful to provide damp-proof course at plinth level to stop the rise of pore water
into the superstructure
Precautions should be taken to keep the rain water away from soaking into the wall so that
the mortar is not softened due to wetness An effective way is to take out roof projections
beyond the walls by about 500 mm
Use of a water-proof plaster on outside face of walls will enhance the life of the building and
maintain its strength at the time of earthquake as well
Ignoring tensile strength free standing walls should be checked against overturning under the
action of design seismic coefficient ah allowing for a factor of safety of 15
1061 भवनो ो की शरतणयाा Categories of Buildings
For the purpose of specifying the earthquake resistant features in masonry and wooden buildings
the buildings have been categorized in five categories A to E based on the seismic zone and the
importance of building I
Where
I = importance factor applicable to the
building [Ref Clause 642 and
Table - 6 of IS 1893 (Part 1) 2002]
The building categories are given in
Table ndash 102
Fig 1013 Cracks at corners of openings in a masonry building ndash reinforcement around them helps
Table -102 Building Categories for Earthquake Resisting Features (IS 4326 1993)
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1062 कमजोर गार म ईोट तचनाई कायय Brickwork in Weak Mortars
The fired bricks should have a compressive strength not less than 35 MPa Strength of bricks
and wall thickness should he selected for the total building height
The mortar should be lime-sand (13) or clay mud of good quality Where horizontal steel is
used between courses cement-sand mortar (13) should be used with thickness so as to cover
the steel with 6 mm mortar above and below it Where vertical steel is used the surrounding
brickwork of 1 X 1 or lfrac12 X 1frac12 brick size depending on wall thickness should preferably be
built using 16 cement-sand mortar
The minimum wall thickness shall be one brick in one storey construction and one brick in
top storey and 1frac12brick in bottom storeys of up to three storey constructions It should also
not be less than l16 of the length of wall between two consecutive perpendicular walls
The height of the building shall be restricted to the following where each storey height shall
not exceed 30 m
For Categories A B and C - three storeys with flat roof and two storeys plus attic pitched
roof
For Category D - two storeys with flat roof and one storey plus attic for pitched roof
1063 आयिाकार तचनाई इकाइयो ो वाला तचनाई तनमायण Masonry Construction with
Rectangular Masonry Units
General requirements for construction of masonry walls using rectangular masonry units are
10631 तचनाई इकाइयाो Masonry Units
Well burnt bricks conforming to IS 1077 1992 or solid concrete blocks conforming to IS
2185 (Part 1) 1979 and having a crushing strength not less than 35 MPa shall be used The
strength of masonry unit required
shall depend on the number of storeys
and thickness of walls
Squared stone masonry stone block
masonry or hollow concrete block
masonry as specified in IS 1597 (Part
2) 1992 of adequate strength may
also be used
10632 गारा Mortar
Mortars such as those given in Table
ndash 103 or of equivalent specification
shall preferably be used for masonry
Table ndash 103 Recommended Mortar Mixes (IS 4326 1993)
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construction for various categories of buildings
Where steel reinforcing bars are provided in masonry the bars shall be embedded with
adequate cover in cement sand mortar not leaner than 13 (minimum clear cover 10 mm) or in
cement concrete of grade M15 (minimum clear cover 15 mm or bar diameter whichever
more) so as to achieve good bond and corrosion resistance
1064 दीवार Walls
Masonry bearing walls built in mortar as specified in 10632 above unless rationally
designed as reinforced masonry shall not be built of greater height than 15 m subject to a
maximum of four storeys when measured from the mean ground level to the roof slab or
ridge level
The bearing walls in both directions shall be straight and symmetrical in plan as far as
possible
The wall panels formed between cross walls and floors or roof shall be checked for their
strength in bending as a plate or as a vertical strip subjected to the earthquake force acting on
its own mass
Note mdash For panel walls of 200 mm or larger thickness having a storey height not more than
35 metres and laterally supported at the top this check need not be exercised
1065 तचनाई बॉणड Masonry Bond
For achieving full strength of
masonry the usual bonds
specified for masonry should be
followed so that the vertical joints
are broken properly from course
to course To obtain full bond
between perpendicular walls it is
necessary to make a slopping
(stepped) joint by making the
corners first to a height of 600
mm and then building the wall in
between them Otherwise the
toothed joint (as shown in Fig
1014) should be made in both the
walls alternatively in lifts of
about 450 mm
Panel or filler walls in framed buildings shall be properly bonded to surrounding framing
members by means of suitable mortar (as given in 10632 above) or connected through
dowels
Fig 1014 Alternating Toothed Joints in Walls at Corner and T-Junction (IS 4326 1993)
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107 ओपतनोग का परभाव Influence of Openings
Openings are functional necessities in buildings
During earthquake shaking inertia forces act in
the strong direction of some walls and in the weak
direction of others Walls shaken in the weak
direction seek support from the other walls ie
walls B1 and B2 seek support from walls A1 and
A2 for shaking in the direction To be more
specific wall B1 pulls walls A1 and A2 while
wall B2 pushes against them
Thus walls transfer loads to each other at their
junctions (and through the lintel bands and roof)
Hence the masonry courses from the walls
meeting at corners must have good interlocking
(Fig 1015) For this reason openings near the
wall corners are detrimental to good seismic
performance Openings too close to wall corners
hamper the flow of forces from one wall to
another Further large openings weaken walls
from carrying the inertia forces in their own
plane Thus it is best to keep all openings as small as possible and as far away from the corners
as possible
108 धारक दीवारो ो म ओपतनोग परदाि करि की सामानय आवशयकताए General Requirements of
Providing Openings in Bearing Walls
Door and window openings in walls reduce their lateral load resistance and hence should
preferably be small and more centrally located The guidelines on the size and position of
opening are given in Table ndash 104 and in Fig 1016
Fig 1015 Regions of force transfer from weak
walls to strong walls in a masonry building ndash Wall
B1 pulls walls A1 and A2 while wall B2pushes walls
A1 and A2
Fig 1016 Dimensions of Openings and Piers for
Recommendations in Table 3 (IS 4326 1993)
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Table ndash 104 Size and Position of Openings in Bearing Walls
S
No
Position of opening Details of Opening for Building Category
A and B C D and E
1 Distance b5 from the inside corner of outside wall Min Zero mm 230 mm 450 mm
2 For total length of openings the ratio (b1+b2+b3)l1 or
(b6+b7)l2 shall not exceed
a) one-storeyed building
b) two-storeyed building
c) 3 or 4-storeyed building
060
050
042
055
046
037
050
042
033
3 Pier width between consecutive openings b4 Min 340 mm 450 mm 560 mm
4 Vertical distance between two openings one above the
other h3 Min
600 mm 600 mm 600 mm
5 Width of opening of ventilator b8 Max 900 mm 900 mm 900 mm
Openings in any storey shall preferably have their top at the same level so that a continuous
band could be provided over them including the lintels throughout the building
Where openings do not comply with the guidelines as given in Table ndash 104 they should be
strengthened by providing reinforced concrete or reinforcing the brickwork as shown in Fig
1017 with high strength deformed (HSD) bars of 8 mm dia but the quantity of steel shall be
increased at the jambs
If a window or ventilator is to be
projected out the projection shall be in
reinforced masonry or concrete and well
anchored
If an opening is tall from bottom to
almost top of a storey thus dividing the
wall into two portions these portions
shall be reinforced with horizontal
reinforcement of 6 mm diameter bars at
not more than 450 mm intervals one on
inner and one on outer face properly tied
to vertical steel at jambs corners or
junction of walls where used
The use of arches to span over the
openings is a source of weakness and
shall be avoided Otherwise steel ties
should be provided
109 भको पी सदढ़ीकरण वयवसथा Seismic Strengthening Arrangements
All masonry buildings shall be strengthened as specified for various categories of buildings as
listed in Table ndash 105
Fig 1017 Strengthening Masonry around Opening (IS
4326 1993)
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Table ndash 105 Strengthening Arrangements Recommended for Masonry Buildings
(Rectangular Masonry Units)(IS 4326 1993)
Building Category Number of Storeyes Strengthening to be Provided in all Storeys
A
i) 1 to 3
ii) 4
a
a b c
B
i) 1 to 3
ii) 4
a b c f g
a b c d f g
C
i) 1 and 2
ii) 3 and 4
a b c f g
a to g
D
i) 1 and 2
ii) 3 and 4
a to g
a to h
E 1 to 3 a to h
Where
a mdash Masonry mortar
b mdash Lintel band
c mdash Roof band and gable band where necessary
d mdash Vertical steel at corners and junctions of walls
e mdash Vertical steel at jambs of openings
f mdash Bracing in plan at tie level of roofs
g mdash Plinth band where necessary and
h mdash Dowel bars
4th storey not allowed in category E
NOTE mdash In case of four storey buildings of category B the requirements of vertical steel may be checked
through a seismic analysis using a design seismic coefficient equal to four times the one given in (a) 3423
of IS 1893 1984 (This is because the brittle behaviour of masonry in the absence of vertical steel results in
much higher effective seismic force than that envisaged in the seismic coefficient provided in the code) If
this analysis shows that vertical steel is not required the designer may take the decision accordingly
The overall strengthening arrangements to be adopted for category D and E buildings which
consist of horizontal bands of reinforcement at critical levels vertical reinforcing bars at corners
junctions of walls and jambs of opening are shown in Fig 1018 amp 1019
Fig 1018 Overall Arrangement of Reinforcing Fig 1019 Overall Arrangement of Reinforcing Masonry
Masonry Buildings (IS 4326 1993) Building having Pitched Roof (IS 4326 1993)
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103
1091 पटट का अनभाग एवो सदढीकरण Section and Reinforcement of Band
The band shall be made of reinforced concrete of grade not leaner than M15 or reinforced
brickwork in cement mortar not leaner than 13 The bands shall be of the full width of the wall
not less than 75 mm in depth and reinforced with steel as indicated in Table ndash 106
Table ndash 106 Recommended Longitudinal Steel in Reinforced Concrete Bands (IS 4326 1993)
Span Building Category
B
Building Category
C
Building Category
D
Building Category
E No of Bars Dia No of Bars Dia No of Bars Dia No of Bars Dia
(1) (2) (3) (4) (5) (6) (7) (8) (9)
m mm mm mm mm
5 or less 2 8 2 8 2 8 2 10
6 2 8 2 8 2 10 2 12
7 2 8 2 10 2 12 4 10
8 2 10 2 12 4 10 4 12
Notes -
1 Span of wall will be the distance between centre lines of its cross walls or buttresses For spans greater than 8 m
it will be desirable to insert pillasters or buttresses to reduce the span or special calculations shall be made to
determine the strength of wall and section of band
2 The number and diameter of bars given above pertain to high strength deformed bars If plain mild-steel bars are
used keeping the same number the following diameters may be used
High Strength Def Bar dia 8 10 12 16 20
Mild Steel Plain bar dia 10 12 16 20 25
3 Width of RC band is assumed same as the thickness of the wall Wall thickness shall be 200 mm minimum A
clear cover of 20 mm from face of wall will be maintained
4 The vertical thickness of RC band be kept 75 mm minimum where two longitudinal bars are specified one on
each face and 150 mm where four bars are specified
5 Concrete mix shall be of grade M15 of IS 456 1978 or 1 2 4 by volume
6 The longitudinal steel bars shall be held in position by steel links or stirrups 6 mm dia spaced at 150 mm apart
NOTE mdash In coastal areas the concrete grade shall be M20 concrete and the filling mortar of 13
(cement-sand with water proofing admixture)
As illustrated in Fig 1020 ndash
In case of reinforced brickwork the
thickness of joints containing steel bars shall
be increased so as to have a minimum
mortar cover of 10 mm around the bar In
bands of reinforced brickwork the area of
steel provided should be equal to that
specified above for reinforced concrete
bands
In category D and E buildings to further
iterate the box action of walls steel dowel
bars may be used at corners and T-junctions
of walls at the sill level of windows to
length of 900 mm from the inside corner in
each wall Such dowel may be in the form of
Fig 1020 Reinforcement and Bending Detail in RC Band ((IS 4326 1993)
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U stirrups 8 mm dia Where used such bars must be laid in 13 cement-sand-mortar with a
minimum cover of 10 mm on all sides to minimize corrosion
1010 भको प क दौरान सटोन तचनाई की दीवारो ो का वयविार Behaviour of Stone Masonry
Walls during Earthquakes
Stone has been used in building construction in India since ancient times since it is durable and
locally available The buildings made of thick stone masonry walls (thickness ranges from 600 to
1200 mm) are one of the most deficient building systems from earthquake-resistance point of
view
The main deficiencies include excessive wall thickness absence of any connection between the
two wythes of the wall and use of round stones (instead of shaped ones) (Fig 1021 amp 1022)
Note A wythe is a continuous vertical section of masonry one unit in thickness A wythe may be
independent of or interlocked with the adjoining wythe (s) A single wythe of brick that is not
structural in nature is referred to as a veneer (httpsenwikipediaorgwikiWythe)
The main patterns of earthquake damage include
(a) bulging separation of walls in the horizontal direction into two distinct wythes
(b) separation of walls at corners and T-junctions
(c) separation of poorly constructed roof from walls and eventual collapse of roof and
(d) disintegration of walls and eventual collapse of the whole dwelling
In the 1993 Killari (Maharashtra) earthquake alone over 8000 people died most of them buried
under the rubble of traditional stone masonry dwellings Likewise a majority of the over 13800
deaths during 2001 Bhuj (Gujarat) earthquake is attributed to the collapse of this type of
construction
1011 भको प परतिरोधी सटोन तचनाई भवन क तनमायण िि सामानय तसदाोि General principle for
construction of Earthquake Resistant stone masonry building
10111 भको प परतिरोधी लकषण Earthquake Resistant Features
1 Low strength stone masonry buildings are weak against earthquakes and should be avoided
in high seismic zones Inclusion of special earthquake-resistant features may enhance the
earthquake resistance of these buildings and reduce the loss of life These features include
Fig 1021 Separation of a thick wall into two layers Fig 1022 Separation of unconnected adjacent walls at junction
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105
(a) Ensure proper wall construction
(b) Ensure proper bond in masonry courses
(c) Provide horizontal reinforcing elements
(d) Control on overall dimensions and heights
2 The mortar should be cement-sand (1 6) lime-sand (1 3) or clay mud of good quality
3 The wall thickness should not be larger than 450
mm Preferably it should be about 350 mm and
the stones on the inner and outer wythes should be
interlocked with each other
NOTE - If the two wythes are not interlocked they
tend to delaminate during ground shaking bulge
apart (as shown in Fig 1023) and buckle
separately under vertical load leading to
complete collapse of the wall and the building
4 The masonry should preferably be brought to courses at not more than 600 mm lift
5 lsquoThroughrsquo stones at full length
equal to wall thickness should be
used in every 600 mm lift at not
more than 12 m apart
horizontally If full length stones
are not available stones in pairs
each of about 34 of the wall
thickness may be used in place of
one full length stone so as to
provide an overlap between them
(as shown in Fig 1024)
6 In place of lsquothroughrsquo stones lsquobonding elementsrsquo of steel bars 8 to 10 mm dia bent to S-shape
or as hooked links may be used with a cover of 25 mm from each face of the wall (as shown
in Fig 1024) Alternatively wood-bars of 38 mm X 38 mm cross section or concrete bars of
50 mm X50 mm section with an 8 mm dia rod placed centrally may be used in place of
throughrsquo stones The wood should be well treated with preservative so that it is durable
against weathering and insect action
7 Use of lsquobondingrsquo elements of adequate length should also be made at corners and junctions of
walls to break the vertical joints and provide bonding between perpendicular walls
8 Height of the stone masonry walls (random rubble or half-dressed) should be restricted as
follows with storey height to be kept 30 m maximum and span of walls between cross walls
to be limited to 50 m
Fig 1023 Wall delaminated with buckled
withes (IS 13828 1993)
Fig 1024 Through Stone and Bond Elements (IS 13828 1993)
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106
a) For categories A and B ndash Two storeys with flat roof or one storey plus attic if walls are
built in lime-sand or mud mortar and -one storey higher if walls are built in cement-sand
1 6 mortar
b) For categories C and D - Two storeys with flat roof or two storeys plus attic for pitched
roof if walls are built in 1 6 cement mortar and one storey with flat roof or one storey
plus attic if walls are built in lime-sand or mud mortar respectively
9 If walls longer than 5 m are needed buttresses may be used at intermediate points not farther
apart than 40 m The size of the buttress be kept of uniform thickness Top width should be
equal to the thickness of main wall t and the base width equal to one sixth of wall height
10 The stone masonry dwellings must have horizontal bands (plinth lintel roof and gable
bands) These bands can be constructed out of wood or reinforced concrete and chosen based
on economy It is important to provide at least one band (either lintel band or roof band) in
stone masonry construction
Note Although this type of stone masonry construction practice is deficient with regards to earthquake
resistance its extensive use is likely to continue due to tradition and low cost But to protect human lives
and property in future earthquakes it is necessary to follow proper stone masonry construction in seismic
zones III and higher Also the use of seismic bands is highly recommended
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107
अधयाय Chapter- 11
भकपीय रलयमकन और रटरोफिट ग
SEISMIC EVALUATION AND RETROFITTING
There are considerable number of buildings that do not meet the requirements of current design
standards because of inadequate design or construction errors and need structural upgrading
specially to meet the seismic requirements
Retrofitting is the best solution to strengthen such buildings without replacing them
111 भकपीय रलयमकन SEISMIC EVALUATION
Seismic evaluation is to assess the seismic response of buildings which may be seismically
deficient or earthquake damaged for their future use The evaluation is also helpful in choosing
appropriate retrofitting techniques
The methods available for seismic evaluation of existing buildings can be broadly divided into
two categories
1 Qualitative methods 2 Analytical methods
1111 गणमतरक िरीक QUALITATIVE METHODS
The qualitative methods are based on the available background information of the structures
past performance of similar structures under severe earthquakes visual inspection report some
non-destructive test results etc
Method for Seismic evaluation
Qualitative methods Analytic methods
CapacityDemand
method
Push over
analysis
Inelastic time
history method
Condition
assessment
Visual
inspection
Non-destructive
testing
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The evaluation of any building is a difficult task which requires a wide knowledge about the
structures cause and nature of damage in structures and its components material strength etc
The proposed methodology is divided into three components
1 Condition assessment
It is based on
data collection or information gathering of structures from architectural and structural
drawings
performance characteristics of similar type of buildings in past earthquakes
rapid evaluation of strength drift materials structural components and structural details
2 Visual inspectionField evaluation It is based on observed distress and damage in
structures Visual inspection is more useful for damaged structures however it may also be
conducted for undamaged structures
3 Non-destructive evaluation It is generally carried out for quick estimation of materials
strength determination of the extent of determination and to establish causes remain out of
reach from visual inspection and determination of reinforcement and its location NDT may
also be used for preparation of drawing in case of non-availability
11111 Condition Assessment for Evaluation
The aim of condition assessment of the structure is the collection of information about the
structure and its past performance characteristics to similar type of structure during past
earthquakes and the qualitative evaluation of structure for decision-making purpose More
information can be included if necessary as per requirement
(i) Data collection information gathering
Collection of the data is an important portion for the seismic evaluation of any existing building
The information required for the evaluated building can be divided as follows
Building Data
Architectural structural and construction drawings
Vulnerability parameters number of stories year of construction and total floor area
Specification soil reports and design calculations
Seismicity of the site
Construction Data
Identifications of gravity load resisting system
Identifications of lateral load resisting system
Maintenance addition alteration or modifications in structures
Field surveys of the structurersquos existing condition
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Structural Data
Materials
Structural concept vertical and horizontal irregularities torsional eccentricity pounding
short column and others
Detailing concept ductile detailing special confinement reinforcement
Foundations
Non-structural elements
(ii) Past Performance data
Past performance of similar type of structure during the earthquake provides considerable amount
of information for the building which is under evaluation process Following are the areas of
concerns which are responsible for poor performance of buildings during earthquake
Material concerns
Low grade on concrete
Deterioration in concrete and reinforcement
High cement-sand ratio
Corrosion in reinforcement
Use of recycled steel as reinforcement
Spalling of concrete by the corrosion of embedded reinforcing bars
Corrosion related to insufficient concrete cover
Poor concrete placement and porous concrete
Structural concerns
The relatively low stiffness of the frames excessive inter-storey drifts damage to non-
structural items
Pounding column distress possibly local collapse
Unsymmetrical buildings (U T L V) in plan torsional effects and concentration of damage
at the junctures (ie re-entrant corners)
Unsymmetrical buildings in elevation abrupt change in lateral resistance
Vertical strength discontinuities concentrate damage in the ldquosoftrdquo stories
Short column
Detailing concerns
Large tie spacing in columns lack of confinement of concrete core shear failures
Insufficient column lengths concrete to spall
Locations of inadequate splices brittle shear failure
Insufficient column strength for full moment hinge capacity brittle shear failure
Lack of continuous beam reinforcement hinge formation during load reversals
Inadequate reinforcing of beam column joints or location of beam bar splices at columns
joint failures
Improper bent-up of longitudinal reinforcing in beams as shear reinforcement shear failure
during load reversal
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Foundation dowels that are insufficient to develop the capacity of the column steel above
local column distress
(iii) Seismic Evaluation Data
Seismic evaluation of data will provide a general idea about the building performance during an
earthquake The criteria of evaluation of building will depend on materials strength and ductility
of structural components and detailing of reinforcement
Material Evaluation
Buildings height gt 3 stories minimum grade concrete M 20 desirable M 30 to M 40
particularly in columns of lower stories
Maximum grade of steel should be Fe 415 due to adequate ductility
No significant deterioration in reinforcement
No evidence of corrosion or spalling of concrete
Structural components
Evaluation of columns shear strength and drift check for permissible limits
Evaluation of plan irregularities check for torsional forces and concentration of forces
Evaluation of vertical irregularities check for soft storey mass or geometric discontinuities
Evaluation of beam-column joints check for strong column-weak beams
Evaluation of pounding check for drift control or building separation
Evaluation of interaction between frame and infill check for force distribution in frames and
overstressing of frames
(i) Flexural members
Limitation of sectional dimensions
Limitation on minimum and maximum flexural reinforcement at least two continuous
reinforced bars at top and bottom of the members
Restriction of lap splices
Development length requirements for longitudinal bars
Shear reinforcement requirements stirrup and tie hooks tie spacing bar splices
(ii) Columns
Limitation of sectional dimensions
Longitudinal reinforcement requirement
Transverse reinforcement requirements stirrup and tie hooks column tie spacing
column bar splices
Special confining requirements
(iii) Foundation
Column steel doweled into the foundation
Non-structural components
Cornices parapet and appendages are anchored
Exterior cladding and veneer are well anchored
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11112 Field Evaluation Visual Inspection Method
The procedure for visual inspection method is as below
Equipments
Optical magnification allows a detailed view of local areas of distress
Stereomicroscope that allow a three dimensional view of the surface Investigator can
estimate the elevation difference in surface features by calibrating the focus adjustment
screw
Fibrescope and borescopes allow inspection of regions that are inaccessible to the naked eye
Tape to measure the dimension of structure length of cracks
Flashlight to aid in lighting the area to be inspected particularly in post-earthquake
evaluation power failure
Crack comparator to measure the width of cracks at representative locations two types
plastic cards and magnifying lens comparators
Pencil to draw the sketch of cracks
Sketchpad to prepare a representation of wall elevation indicating the location of cracks
spalling or other damage records of significant features such as non-structural elements
Camera for photographs or video tape of the observed cracking
Action
Perform a walk through visual inspection to become familiar with the structure
Gather background documents and information on the design construction maintenance
and operation of structure
Plan the complete investigation
Perform a detailed visual inspection and observe type of damage cracks spalls and
delaminations permanent lateral displacement and buckling or fracture of reinforcement
estimating of drift
Observe damage documented on sketches interpreted to assess the behaviour during
earthquake
Perform any necessary sampling basis for further testing
Data Collection
To identify the location of vertical structural elements columns and walls
To sketch the elevation with sufficient details dimensions openings observed damage such
as cracks spalling and exposed reinforcing bars width of cracks
To take photographs of cracks use marker paint or chalk to highlight the fine cracks or
location of cracks in photographs
Observation of the non-structural elements inter-storey displacement
Limitations
Applicable for surface damage that can be visualised
No identification of inner damage health monitoring of building chang of frequency and
mode shapes
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11113 Non-destructive testing (NDT)
Visual inspection has the obvious limitation that only visible surface can be inspected Internal
defects go unnoticed and no quantitative information is obtained about the properties of the
concrete For these reasons a visual inspection is usually supplemented by NDT methods Other
detailed testing is then conducted to determine the extent and to establish causes
NDT tests for condition assessment of structures
Some methods of field and laboratory testing that may assess the minimum concrete strength and
condition and location of the reinforcement in order to characterize the strength safety and
integrity are
(i) Rebound hammer Swiss hammer
The rebound hammer is the most widely used non-destructive device for quick surveys to assess
the quality of concrete In 1948 Ernest Schmidt a Swiss engineer developed a device for testing
concrete based upon the rebound principal strength of in-place concrete comparison of concrete
strength in different locations and provides relative difference in strength only
Limitations
Not give a precise value of compressive strength provide estimate strength for comparison
Sensitive to the quality of concrete carbonation increases the rebound number
More reproducible results from formed surface rather than finished surface smooth hard-
towelled surface giving higher values than a rough-textured surface
Surface moisture and roughness also affect the reading a dry surface results in a higher
rebound number
Not take more than one reading at the same spot
(ii) Penetration resistance method ndash Windsor probe test
Penetration resistance methods are used to determine the quality and compressive strength of in-
situ concrete It is based on the determination of the depth of penetration of probes (steel rods or
pins) into concrete by means of power-actuated driver This provides a measure of the hardness
or penetration resistance of the material that can be related to its strength
Limitations
Both probe penetration and rebound hammer test provide means of estimating the relative
quality of concrete not absolute value of strength of concrete
Probe penetration results are more meaningful than the results of rebound hammer
Because of greater penetration in concrete the prove test results are influenced to a lesser
degree by surface moisture texture and carbonation effect
Probe test may be the cause of minor cracking in concrete
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(iii) Rebar locatorconvert meter
It is used to determine quantity location size and condition of reinforcing steel in concrete It is
also used for verifying the drawing and preparing as-built data if no previous information is
available These devices are based on interaction between the reinforcing bars and low frequency
electromagnetic fields Commercial convert meter can be divided into two classes those based
on the principal of magnetic reluctance and those based on eddy currents
Limitations
Difficult to interpret at heavy congestion of reinforcement or when depth of reinforcement is
too great
Embedded metals sometimes affect the reading
Used to detect the reinforcing bars closest to the face
(iv) Ultrasonic pulse velocity
It is used for determination the elastic constants (modulus of elasticity and Poissonrsquos ratio) and
the density By conducting tests at various points on a structure lower quality concrete can be
identified by its lower pulse velocity Pulse-velocity measurements can detect the presence of
voids of discontinuities within a wall however these measurements can not determine the depth
of voids
Limitations
Moisture content an increase in moisture content increases the pulse velocity
Presence of reinforcement oriented parallel to the pulse propagation direction the pulse may
propagate through the bars and result is an apparent pulse velocity that is higher than that
propagating through concrete
Presence of cracks and voids increases the length of the travel path and result in a longer
travel time
(v) Impact echo
Impact echo is a method for detecting discontinuities within the thickness of a wall An impact-
echo test system is composed of three components an impact source a receiving transducer and
a waveform analyzer or a portable computer with a data acquisition
Limitations
Accuracy of results highly dependent on the skill of the engineer and interpreting the results
The size type sensitivity and natural frequency of the transducer ability of FFT analyzer
also affect the results
Mainly used for concrete structures
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(vi) Spectral analysis of surface waves (SASW)
To assess the thickness and elastic stiffness of material size and location of discontinuities
within the wall such as voids large cracks and delimitations
Limitations
Interpretation of results is very complex
Mainly used on slab and other horizontal surface to determine the stiffness profiles of soil
sites and of flexible and rigid pavement systems measuring the changes in elastic properties
of concrete slab
(vii) Penetrating radar
It is used to detect the location of reinforcing bars cracks voids or other material discontinuities
verify thickness of concrete
Limitations
Mainly used for detecting subsurface condition of slab-on-grade
Not useful for detecting the small difference in materials
Not useful for detecting the size of bars closely spaced bars make difficult to detect features
below the layer of reinforcing steel
1112 ववशलषणमतरक िरीक ANALYTICAL METHODS
Analytical methods are based on considering capacity and ductility of the buildings which are
based on detailed dynamic analysis of buildings The methods in this category are
capacitydemand method pushover analysis inelastic time history analysis etc Brief discussions
on the method of evaluation are as follows
11121 CapacityDemand (CD) method
The forces and displacements resulting from an elastic analysis for design earthquake are
called demand
These are compared with the capacity of different members to resist these forces and
displacements
A (CD) ratio less than one indicate member failure and thus needs retrofitting
When the ductility is considered in the section the demand capacity ratio can be equated to
section ductility demand of 2 or 3
The main difficulty encountered in using this method is that there is no relationship between
member and structure ductility factor because of non-linear behaviour
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11122 Push Over Analysis
The push over analysis of a structure is a static non-linear analysis under permanent vertical
loads and gradually increasing lateral loads
The equivalent static lateral loads approximately represent earthquake-induced forces
A plot of total base shear verses top displacement in a structure is obtained by this analysis
that would indicate any premature failure or weakness
The analysis is carried out up to failure thus it enables determination of collapse load and
ductility capacity
On a building frame loaddisplacement is applied incrementally the formation of plastic
hinges stiffness degradation and plastic rotation is monitored and lateral inelastic force
versus displacement response for the complete structure is analytically computed
This type of analysis enables weakness in the structure to be identified The decision to
retrofit can be taken on the basis of such studies
11123 Inelastic time-history analysis
A seismically deficient building will be subjected to inelastic action during design earthquake
motion
The inelastic time history analysis of the building under strong ground motion brings out the
regions of weakness and ductility demand in the structure
This is the most rational method available for assessing building performance
There are computer programs available to perform this type of analysis
However there are complexities with regard to biaxial inelastic response of columns
modelling of joints behaviour interaction of flexural and shear strength and modelling of
degrading characteristics of member
The methodology is used to ascertain deficiency and post-elastic response under strong
ground shaking
Fig ndash 111 Strengthening strategies
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112 भवनो की रटरोफिट ग Retrofitting of Building
Retrofitting is to upgrade the strength and structural capacity of an existing structure to enable it
to safely withstand the effect of strong earthquakes in future
1121 सकटरचरल लवल यम गलोबल रटरोफि िरीक Structural Level or Global Retrofit
Methods
Two approaches are used for structural-level retrofitting
(i) Conventional Methods
(ii) Non-conventional methods
Retrofit procedure
Detailed seismic
evaluation
Retrofit
techniques
Seismic capacity
assessment
Selection of retrofit
scheme
Design of retrofit
scheme and detailing
Re-evaluation of
retrofit structure
Addition of infill walls
Addition of new
external walls
Addition of bracing
systems
Construction of wing
walls
Strengthening of
weak elements
Structural Level or Global Member Level or Local
Seismic Base Isolation
Jacketing of beams
Jacketing of columns
Jacketing of beam-
column joints
Strengthening of
individual footings
Seismic Dampers
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11211 Conventional Methods
Conventional Methods are based on increasing the seismic resistance of existing structure The
main categories of these methods are as follow
a) Addition of infilled walls
b) Addition of new external walls
c) Addition of bracing system
d) Construction of wing walls
e) Strengthening of weak elements
112111 Addition of infilled walls
The construction of infill walls within the frames of the load bearing structures as shown in the
example of Fig ndash 112 aims to drastically increase the strength and the stiffness of the structure
This method can also be applied in order to correct design errors in the structure and more
specifically when a large asymmetric distribution of strength or stiffness in elevation or an
eccentricity of stiffness in plan have been recognised
Fig - 112 Addition of infilled wall and wing walls
Fig - 113 Frames and shear wall
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As shown in Fig ndash 114 there are two alternatives methods of adding infill walls Either the infill
wall is simply placed between two existing columns or it is extended around the columns to form
a jacket The second method is specifically recommended in order to increase the strength in this
region In the situation where the existing columns are very weak a steel cage should be placed
around the columns before constructing new walls and column jackets In all cases the base of
any new wall should always be connected to the existing foundation
112112 Addition of new external walls
In some cases strengthening by adding concrete walls can be performed externally This can
often be carried out for functional reasons as for example in cases when the building must be
kept in operation during the intervention works New cast-in-place concrete walls constructed
outside the building can be designed to resist part or all the total seismic forces induced in the
building The new walls are preferably positioned adjacent to vertical elements (columns or
walls) of the building and are connected to the structure by placing special compression tensile
or shear connectors at every floor level of the building As shown in Figure 115 new walls
usually have a L-shaped cross-section and are constructed to be in contact with the external
corners of the building
Fig ndash 114 Two alternative methods of adding infill walls
Fig ndash 115 Schematic arrangement of connections between the existing building and
a new wall (a) plan (b) section of compression connector and (c) section of tension
connector
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It is important to ensure that connectors behave elastically under seismic design action effects
For this reason when designing the connectors a resistance safety factor equal to 14 is
recommended The use of compression and tensile connectors instead of shear connectors is
strongly recommended as much higher forces can be transferred It is essential that the anchorage
areas for the connectors on the existing
building and on the new walls have
enough strength to guarantee the transfer
of forces between new walls and the
existing structures
A very important issue of the above
method concerns the foundation of new
walls Foundation conditions should be
improved if large axial forces can be
induced in new walls during seismic
excitation In addition the construction
of short cantilever beams protruding from
the wall underneath the adjacent beams
at every floor level of the building as
shown in Fig ndash 116 appears to be a good solution
112113 Addition of bracing systems
The construction of bracing within
the frames of the load bearing
structure aims for a high increase
in the stiffness and a considerable
increase in the strength and
ductility of the structure Bracing
is normally constructed from steel
elements rather than reinforced
concrete as the elastic
deformation of steel aids the
absorption of seismic energy
Bracing systems can be used in a similar way as that for
steel constructions and can be applied easily in single-
storey industrial buildings with a soft storey ground floor
level where no or few brick masonry walls exist between
columns
Various truss configurations have been applied in
practice examples of which are K-shaped diamond
shaped or cross diagonal The latter is the most common
and is often the most effective solution
Fig ndash 116 Construction of cantilever beams to
transfer axial forces to new walls (a) plan (b)
section c-c
Fig ndash 117 Reinforced Concrete Building retrofitted
with steel bracing
Fig ndash 118 Steel bracing soft storey
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Use of steel bracing has a potential advantage over other schemes for the following reasons
Higher strength and stiffness can be proved
Opening for natural light can be
made easily
Amount of work is less since
foundation cost may be minimised
Bracing system adds much less
weight to the existing structure
Most of the retrofitting work can
be performed with prefabricated
elements and disturbance to the
occupants may be minimised
112114 Construction of wing wall
The construction of reinforced
concrete wing walls in continuous
connection with the existing columns
of a structure as shown above in
example of Fig ndash 112 is a very
popular technique
As presented in Fig ndash 1110 there are
two alternative methods of connecting
the wing wall to the existing load
bearing structure
In the first method the wall is connected to the column and the beams at the top and the base
of any floor level Steel dowels or special anchors are used for the connection and the
reinforcement of the new wall is welded to the existing reinforcement
In the second method the new wing wall is extended around the column to form a jacket
Obviously in this case stresses at the interface between the new concrete and the existing
column are considerably lower when compared to the first method
Moreover uncertainties regarding the capacity of the connection between the wall and the
column do not affect the seismic performance of the strengthened element Therefore the second
alternative method is strongly recommended
Fig ndash 1110 Construction of reinforced concrete wing
wall
Fig ndash 119 Steel bracing
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112115 Strengthening weak elements
The selective strengthening of weak elements of the
structure aims to avoid a premature failure of the critical
elements of a building and to increase the ductility of the
structure
Usually this method is applied to vertical elements and
is accompanied by the construction of fibre reinforced
polymer (FRP) jackets or as shown in Fig- 1111 steel
cages around the vertical elements
If a strength increase is also required this method can
include the construction of column jackets of shotcrete
or reinforced concrete
11212 Non-conventional methods
These are based on reduction of seismic demands Seismic demands are the force and
displacement resulting from an elastic analysis for earthquake design Incorporation of energy
absorbing systems to reduce seismic demands are as follows
(i) Seismic Base Isolation
(ii) Seismic Dampers
112121 Seismic Base Isolation
Isolation of
superstructure from the
foundation is known as
base isolation
It is the most powerful
tool for passive
structural vibration
control technique
Types of base isolations
Elastomeric Bearings
This is the most widely used Base Isolator
The elastomer is made of either Natural Rubber or Neoprene
The structure is decoupled from the horizontal components of the earthquake ground motion
Fig ndash 1111 Construction of a steel
cage around a vertical element
Fig ndash 1112 Base isolated structures
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Sliding System
a) Sliding Base Isolation Systems
It is the second basic type of isolators
This works by limiting the base shear across the
isolator interface
b) Spherical Sliding Base Isolators
The structure is supported by bearing pads that
have curved surface and low friction
During an earthquake the building is free to
slide on the bearings
c) Friction Pendulum Bearing
These are specially designed base isolators
which works on the
principle of simple
pendulum
It increases the natural time
period of oscillation by
causing the structure to
Fig ndash 1113 Elastomeric Isolators Fig ndash 1114 Steel Reinforced Elastomeric
Isolators
Fig ndash 1115 Metallic Roller Bearing
Fig ndash 1116 Spherical Sliding Base
Isolators
Fig ndash 1117 Cross-section of Friction Pendulum Bearing
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slide along the concave inner surface through the frictional interface
It also possesses a re-centering capability
Typically bearings measure 10 m (3 feet) in dia 200 mm (8 inches) in height and weight
being 2000 pounds
d) Advantages of base isolation
Isolate building from ground motion
Building can remain serviceable throughout construction
Lesser seismic loads hence lesser damage to the structure
Minimal repair of superstructure
Does not involve major intrusion upon existing superstructure
e) Disadvantages of base isolation
Expensive
Cannot be applied partially to structures unlike other retrofitting
Challenging to implement in an efficient manner
Allowance for building displacements
Inefficient for high rise buildings
Not suitable for buildings rested on soft soil
112122 Seismic Dampers
Seismic dampers are used in place of structural elements like diagonal braces for controlling
seismic damage in structures
It partly absorbs the seismic energy and reduces the motion of buildings
Types
Viscous Dampers Energy is absorbed by silicon-based fluid passing between piston-
cylinder arrangement
Fig -1118 Cross-section of a Viscous Fluid Damper
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Friction Dampers Energy is absorbed
by surfaces with friction between
rubbing against each other
Yielding Dampers Energy is absorbed
by metallic components that yield
1122 सदसकय सकिर यम सकथमनीय ररटरोफमइ िरीक Member Level or Local Retrofit Methods
The member level retrofit or local retrofit approach is to upgrade the strength of the members
which are seismically deficient This approach is more cost effective as compared to the
structural level retrofit
Jacketing
The most common method of enhancing the individual member strength is jacketing It includes
the addition of concrete steel or fibre reinforced polymer (FRP) jackets for use in confining
reinforced concrete columns beams joints and foundation
Types of jacketing
(1) Concrete jacketing (2) Steel jacketing (3) Strap jacketing
Fig ndash 1119 Friction Dampers
Fig ndash 1120 Yielding Dampers
Fig ndash 1121 Type of Jacketing
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11221 Member level Jacketing
(i) Jacketing of Columns
Different methods of column jacketing are as shown in Figures below
Fig ndash 1122 (b) Column with
CFRP (Carbon Fibre
Reinforced Polymer) Wrap
Fig ndash 1122 (c) Column with Steel Fig ndash 1122 (d) Column with
Jacketing Steel Caging
Fig ndash 1122 (a) Reinforced Concrete Jacketing
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Fig ndash 1122 (e) Construction techniques for Fig ndash 1122 (f) Local strengthening of RC
column jacketing Columns
Fig ndash 1122 (g) Details for provision of longitudinal reinforcement
Fig ndash 1122 (h) Different methods of column jacketing
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(ii) Jacketing of Beam
(iii) Jacketing of Beam-Column Joint
Fig ndash 1123 Different ways of beam jacketing
Fig ndash 1124 Continuity of longitudinal steel in jacketed beams
Fig ndash 1125 Steel cage assembled in the joint
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11222 Table showing the details of reinforced concrete jacketing
Properties of jackets match with the concrete of the existing structure
compressive strength greater than that of the existing
structures by 5 Nmm2 (50 kgcm
2) or at least equal to that
of the existing structure
Minimum width of
jacket 10 cm for concrete cast-in-place and 4 cm for shotcrete
If possible four sided jacket should be used
A monolithic behaviour of the composite column should be
assured
Narrow gap should be provided to prevent any possible
increase in flexural capacity
Minimum area of
longitudinal
reinforcement
3Afy where A is the area of contact in cm2 and fy is in
kgcm2
Spacing should not exceed six times of the width of the new
elements (the jacket in the case) up to the limit of 60 cm
Percentage of steel in the jacket with respect to the jacket
area should be limited between 0015 and 004
At least a 12 mm bar should be used at every corner for a
four sided jacket
Minimum area of
transverse
reinforcement
Designed and spaced as per earthquake design practice
Minimum bar diameter used for ties is not less than 10 mm
diameter anchorage
Due to the difficulty of manufacturing 135 degree hooks on
the field ties made up of multiple pieces can be used
Shear stress in the
interface Provide adequate shear transfer mechanism to assured
monolithic behaviour
A relative movement between both concrete interfaces
(between the jacket and the existing element) should be
prevented
Chipping the concrete cover of the original member and
roughening its surface may improve the bond between the
old and the new concrete
For four sided jacket the ties should be used to confine and
for shear reinforcement to the composite element
For 1 2 3 side jackets as shown in Figures special
reinforcement should be provided to enhance a monolithic
behaviour
Connectors Connectors should be anchored in both the concrete such that
it may develop at least 80 of their yielding stress
Distributed uniformly around the interface avoiding
concentration in specific locations
It is better to use reinforced bars (rebar) anchored with epoxy
resins of grouts as shown in Figure (a)
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11223 Practical aspects in choosing appropriate techniques
Certain issues of practical importance that may help to avoid mistakes in choosing the
appropriate technique are as follows
1) The strengthening of columns by using FRPs or steel jackets is unsuitable for flexible
structures where failure would be controlled by deflection In this case the strengthening
should aim to increase the stiffness
2) It is not favourable to use steel cages or confine with FRPs when an increase in the flexural
capacity of vertical elements is required
3) The application of confinement (with FRPs or steel) to circular or rectangular columns would
increase the ductility and the shear strength and would limit the slippage of overlapping bars
when the lap length has been found to be insufficient However a significant contribution
cannot be expected for columns of rectangular cross section with a large aspect ratio or those
with L-shaped cross sections
4) In the case of columns that have heavily rusted reinforcement strengthening with FRP
jackets (or the application of epoxy glue) will protect the reinforcement from further
oxidation However if the corrosion of the reinforcement is at an advanced stage it is
probable that strengthening may not stop the premature failure of the element
5) The construction of FRP jackets around vertical elements will increase the ductility but it
cannot increase the buckling resistance of the longitudinal reinforcement bars Thus if the
stirrups are too thin in an existing element failure will probably result from the premature
bending of the vertical reinforcement In this case local stress concentrations from the
distressed bars will build up between the stirrups and will lead to a local failure of the jacket
Consequently if bending of the vertical reinforcement has been evaluated as the most likely
cause of column failure the preferable choice for strengthening of the element would be to
place a steel cage
6) In areas where the overlapping of reinforcement bars has been found to be inadequate (short
lap lengths) confining the element with FRPs steel cages or steel jackets will improve the
strength and the ductility of the region considerably However even if it improved the
behaviour it is eventually unfeasible to deter the slipping of bars Consequently when the lap
length of bars has been found to be smaller than 30 of code requirements the solution of
welding of bars must be selected Moreover it must be pointed out that confinement cannot
offer anything to longitudinal bars that are not in the corners of the cross section
7) Experimentally the procedure of placing FRP sheets to strengthen weak beam-column joints
has proved to be particularly effective In practice however this technique has been found to
be difficult to apply due to the presence of slabs and transverse beams The same problems
arise when placing steel plates Other techniques such as the construction of reinforced
concrete jackets or the reconstruction of joints with additional interior reinforcement appear
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to be more beneficial In cases where only a light damage to the joints has been found
repairing with an epoxy resin appears to be particularly effective solution
8) The placing of new concrete in contact with an existing element (by shotcreting and
especially by pouring) will require prior aggravation of the old surface to a depth of at least 6
mm This should be performed by sandblasting or by using suitable mechanical equipment
(for example a scabbler and not just simply a hammer and a chisel) This is to remove the
exterior weak skin of the concrete and to expose the aggregate
9) When placing a new concrete jacket around an existing column it is not always possible to
follow code requirements and place
internal rectangular stirrups to enclose
the middle longitudinal bars as shown
in Fig-1126(a) In this case it is
proposed to place two middle bars in
each side of the jacket so that
octagonal stirrups can be easily
placed as demonstrated in
Fig-1126(b)
In the case where columns have a cross section
with a large aspect ratio the middle longitudinal
bars can be connected by drilling holes through
the section in order to place a S-shaped stirrup as
shown in Fig ndash 1127 After placing stirrups the
remaining void can be filled with epoxy resin In
order to ease placement the S-shaped stirrup can
be prefabricated with one hook and after placing
the second hook can be formed by hand
10) If a thin concrete jacket is to be
placed around a vertical element
and the 135 deg hooks at the ends
of the stirrups are impeded by the
old column it would be
acceptable to decrease the hook
anchorage from 10 times the bar
diameter to 5 or 6 times the bar
diameter as shown in
Fig ndash 1128(a) Otherwise the
ends the stirrups should be
welded together or connected
with special contacts (clamps) as
presented in Fig ndash 1128(b) that have now appeared on the market
(a) (b)
Fig ndash 1126 Placement of internal stirrups in
rectangular cross section
Fig ndash 1127 Placement of an internal
stirrup in a rectangular cross section
with a large aspect ratio
(a) (b)
Fig ndash 1128 Reducing hook lengths and welding the
ends of stirrups
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11) When constructing a jacket around a column it is
important to also strengthen the column joint As shown
in Fig ndash 1129 this can be accomplished by where
possible extending the longitudinal reinforcement bars
around the joint In addition as also shown in
Fig ndash 1129 stirrups must be placed in order to confine
the concrete of the jacket around the joint
In the case where the joint has been found to be
particularly weak a steel diagonal collar can be placed
around the joint before placing the reinforcement as
shown in Fig ndash 1130
12) It is preferable that a new concrete jacket is placed
continuously from the foundation to the top of the building
If this is not possible (due to maintaining the functioning of
the building) it is usual to stop the jacket at the top of the
ground floor level In this case there is a need to anchor the
jacketrsquos longitudinal bars to the existing column This can
be achieved by anchoring a steel plate to the base of the
column of the floor level above and then welding the
longitudinal bars to the anchor plate as shown in Fig ndash
1131
13) In the case where there is a need to reconstruct a heavily damaged column after first shoring
up the column all the defective concrete must be removed so that only good concrete
Fig ndash 1129 Strengthening the
column joint
Fig ndash 1130 Placing a steel diagonal collar
around a weak column joint
Fig ndash 1131 Removal of
defective concrete from a
heavily damaged column
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remains as shown in Fig ndash 1132 Any
buckled reinforcement bars must be welded
to the existing bars Finally the column can
be recast by placing a special non-shrink
concrete
14) In order to anchor new reinforcement bars dowels or anchors with the use of epoxy glue the
diameter of holes drilled into the existing concrete should be roughly 4 mm larger than the
diameter of the bar The best way to remove dust from drilled holes would be to spray water
at the back of the hole The best results (higher adhesive forces) are achieved when the walls
of the hole have been roughened slightly with a small wire brush
15) Care is required when shotcreting in the presence of reinforcement There is a danger of an
accumulation of material building up behind the bars This is usually accredited to material
sticking to the face of bars and may be due to either a low velocity a large firing distance or
insufficient pressure from the compressor
16) The placing of steel plates and especially FRP sheets or fabrics requires special preparation of
the concrete surface to which they will be stuck The rounding of corners and the removal of
surface abnormalities constitute minimal conditions for the application of this technique
17) Two constructional issues that concern the connection of new walls to the old frame require
particular attention The first problem is due to the shrinkage of the new concrete and the
appearance of cracks at the top of the new wall immediately below the old beam in the
region where a good contact between surfaces is essential Here the problem of shrinkage
can be usually dealt with by placing concrete of a particular composition where special
admixtures (for example expansive cements) have been used Alternatively the new wall
could be placed to about 20 cm below the existing beam and after more than 7 days (taking
into account temperature and how new concrete shrinks with time) the void can be filled
with an epoxy or polyster mortar In some cases depending on site conditions (ease of access
dry conditions etc) the new wall can be placed to a height of 2 to 5 mm below the beam and
the void filled with resin glue using the technique of resin injection The second problem
concerns the case of walls from ready-mix concrete and the difficulty of placing the higher
part of the wall due to insufficient access For this reason alone the use of shotcrete should
be the preferred option
Fig ndash 1132 Welding longitudinal bars to an
anchor plate
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113 आरसी भवनो क घ को र समरमनय भकपी कषतियम और उनक उपचमर Common
seismic damage in components of RC Buildings and their remedies
Possible damages in component of RC Buildings which are frequently observed after the
earthquakes are as follows
(i) R C Column
The most common modes of failure of column are as follows
Mode -1 Formation of plastic hinge at the base of ground level columns
Mechanism The column when subjected to seismic
motion its concrete begins to disintegrate and the
load carried by the concrete shifts to longitudinal
reinforcement of the column This additional load
causes buckling of longitudinal reinforcement As a
result the column shortens and looses its ability to
carry even the gravity load
Reasons Insufficient confinement length and
improper confinement in plastic hinge region due to
smaller numbers of ties
Remedies This type of damage is sensitive to the cyclic moments generated during the
earthquake and axial load intensity Consideration is to be paid on plastic hinge length or length
of confinement
Mode ndash 2 Diagonal shear cracking in mid span of columns
Mechanism In older reinforced
concrete building frames column
failures were more frequent since
the strength of beams in such
constructions was kept higher than
that of the columns This shear
failure brings forth loss of axial
load carrying capacity of the
column As the axial capacity
diminishes the gravity loads carried by the column are transferred to neighbouring elements
resulting in massive internal redistribution of forces which is also amplified by dynamic effects
causing spectacular collapse of building
Reason Wide spacing of transverse reinforcement
Remedies To improve understanding of shear strength as well as to understand how the gravity
loads will be supported after a column fails in shear
Fig ndash 1133 Formation of plastic hinge at
the base
Fig ndash 1134 Diagonal shear cracking in mid span of
columns
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Mode ndash 3 Shear and splice failure of longitudinal reinforcement
Mechanism Splices of column
longitudinal reinforcement in
older buildings were
commonly designed for
compression only with
relatively light transverse
reinforcement enclosing the
lap
Under earthquake motion the
longitudinal reinforcement may
be subjected to significant tensile stresses which require lap lengths for tension substantially
exceeding those for compression As a result slip occurs along the splice length with spalling of
concrete
Reasons Deficient lap splices length of column longitudinal reinforcement with lightly spaced
transverse reinforcement particularly if the splices just above the floor slab especially the splices
just above the floor slab which is very common in older construction
Remedies Lap splices should be provided only in the center half of the member length and it
should be proportionate to tension splice Spacing of transverse reinforcement as per IS
139291993
Mode ndash 4 Shear failures in captive columns and short columns
Captive column Column whose deforming ability is restricted and only a fraction of its height
can deform laterally It is due to presence of adjoining non-structural elements columns at
slopping ground partially buried basements etc
Fig - 1135 Shear and splice failure of longitudinal
reinforcement
Fig ndash 1136 Restriction to the Lateral
Displacement of a Column Creating a Captive-
Column Effect
Fig ndash 1137 Captive-column effect in a
building on sloping terrain
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A captive column is full storey slender column whose clear height is reduced by its part-height
contact with a relatively stiff non-structural element such as a masonry infill wall which
constraints its lateral deformation over
the height of contract
The captive column effect is caused by
a non-intended modification to the
original structural configuration of the
column that restricts the ability of the
column to deform laterally by partially
confining it with building components
The column is kept ldquocaptiverdquo by these
components and only a fraction of its
height can deform laterally
corresponding to the ldquofreerdquo portion
thus the term captive column Figure
as given below shows this situation
Short column Column is made shorter than neighbouring column by horizontal structural
elements such as beams girder stair way landing slabs use of grade beams and ramps
Fig ndash 1138 Typical captive-column failure Fig ndash 1139 Column damage due to
captive- column effect
Fig ndash 1140 Captive column caused by ventilation
openings in a partially buried basement
Fig ndash 1141 Short column created by
a stairway landing
Fig ndash 1142 Shear failures in captive columns
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For split-level buildings in order to circumvent the short-column effect the architect should
avoid locating a frame at the vertical plane where the transition between levels occurs For
buildings on slopes special care should be exercised to locate the sloping retaining walls in such
a way that no captive-column effects are induced Where stiff non-structural walls are still
employed these walls should be separated from the structure and in no case can they be
interrupted before reaching the full height of the adjoining columns
Mechanism A reduction in the clear height of captive or short columns increases the lateral
stiffness Therefore these columns are subjected to larger shear force during the earthquake since
the storey shear is distributed in proportion to lateral stiffness of the same floor If these columns
reinforced with conventional longitudinal and transverse reinforcement and subjected to
relatively high axial loading fail by splitting of concrete along their diagonals if the axial
loading level is low the most probable mode of failure is by shear sliding along full depth cracks
at the member ends Moreover in the case of captive column is so effective that usually damage
is shifted to the short non-confined upper section of the column
Reasons Large shear stresses when the structure is subjected to lateral forces are not accounted
for in the standard frame design procedure
Remedies The best solution for captive column or short column is to avoid the situation
otherwise use separation gap in between the non-structural elements and vertical structural
element with appropriate measures against out-of-plane stability of the masonry wall
(ii) R C Beams
The shear-flexure mode of failure is most commonly observed during the earthquakes which is
described as below
Mode ndash 5 Shear-flexure failure
Mechanism Two types of plastic hinges may form in the beams of multi-storied framed
construction depending upon the span of
beams In case of short beams or where
gravity load supported by the beam is
low plastic hinges are formed at the
column ends and damage occurs in the
form of opening of a crack at the end of
beam otherwise there is formation of
plastic hinges at and near end region of
beam in the form of diagonal shear
cracking
Reasons Lack of longitudinal compressive reinforcement infrequent transverse reinforcement in
plastic hinge zone bad anchorage of the bottom reinforcement in to the support or dip of the
longitudinal beam reinforcement bottom steel termination at face of column
Fig ndash 1143 Shear-flexure failure
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Remedies Adequate flexural and shear strength must be provided and verification by design
calculation is essential The beams should not be too stiff with respect to adjacent columns so
that the plastic hinging will occur in beam rather than in column To ensure that the plastic hinges
zones in beams have adequate ductility the following considerations must be considered
Lower and upper limits on the amount of longitudinal flexural tension steel
A limit on the ration of the steel on one side of the beam to that of on the other side
Minimum requirements for the spacing and size of stirrups to restrain buckling of the
longitudinal reinforcement
(iii) R C Beam-Column Joints
The most common modes of failure in beam-column joint are as follows
Mode ndash 6 shear failure in beam-column joint
Mechanism The most common
failure observed in exterior joints are
due to either high shear or bond
(anchorage) under severe
earthquakes Plastic hinges are
formed in the beams at the column
faces As a result cracks develop
throughout the overall beam depth
Bond deterioration near the face of
the column causes propagation of
beam reinforcement yielding in the joint and a shortening of the bar length available for force
transfer by bond causing horizontal bar slippage in the joint In the interior joint the beam
reinforcement at both the column faces undergoes different stress conditions (compression and
tension) because of opposite sights of seismic bending moments results in failure of joint core
Reasons Inadequate anchorage of flexural steel in beams lack of transverse reinforcement
Remedies Exterior Joint ndash The provision on anchorage stub for the beam reinforcement
improves the performance of external joints by preventing spalling of concrete cover on the
outside face resulting in loss of flexural strength of the column This increases diagonal strut
action as well as reduces steel congestion as the beam bars can be anchored clear of the column
bars
(iv) R C Slab
Generally slab on beams performed well during earthquakes and are not dangerous but cracks in
slab creates serious aesthetic and functional problems It reduces the available strength stiffness
and energy dissipation capacity of building for future earthquake In flat slab construction
punching shear is the primary cause of failure The common modes of failure are
Fig - 1144 Shear failure in beam-column joint
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Mode ndash 7 Shear cracking in slabs
Mechanism Damage to slab oftenly
occurs due to irregularities such as large
openings at concentration of earthquake
forces close to widely spaced shear
walls at the staircase flight landings
Reasons Existing micro cracks which
widen due to shaking differential
settlement
Remedies
Use secondary reinforcement in the bottom of the slab
Avoid the use of flat slab in high seismic zones provided this is done in conjunction with a
stiff lateral load resisting system
(v) R C Shear Walls
Shear walls generally performed well during the earthquakes Four types of failure modes are
generally observed
Mode ndash 8 Four types of failure modes are generally observed
(i) Diagonal tension-compression failure in the form of cross-shaped shear cracking
(ii) Sliding shear failure cracking at interface of new and old concrete
(iii) Flexure and compression in bottom end region of wall and finally
(iv) Diagonal tension in the form of X shaped cracking in coupling beams
Fig ndash 1145 Shear cracking in slabs
Fig ndash 1146 Diagonal tension-compression Sliding shear Flexure and compression
failure
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Mechanism Shear walls are subjected to shear and flexural deformation depending upon the
slenderness ratio Therefore the damage in shear walls may generally occurs due to inadequate
shear and flexure capacity of wall Slender walls are governed by their flexural strength and
cracking occurs in the form of yielding of main flexure reinforcement in the plastic hinge region
normally at the base of the wall Squat walls are governed by their shear strength and failure
takes place due to diagonal tension or diagonal compression in the form of inclined cracking
Coupling beams between shear walls or piers may also damage due to inadequate shear and
flexure capacity Sometimes damage occurs at the construction joints in the form of slippage and
related drift
Reasons
Flexuralboundary compression failure Inadequate transverse confining reinforcement to the
main flexural reinforcement near the outer edge of wall in boundary elements
Flexurediagonal tension Inadequate horizontal shear reinforcement
Sliding shear Absence of diagonal reinforcement across the potential sliding planes of the
plastic hinge zone
Coupling beams Inadequate stirrup reinforcement and no diagonal reinforcement
Construction joint Improper bonding between two surfaces
Remedies
The concrete shear walls must have boundary elements or columns thicker than walls which
will carry the vertical load after shear failure of wall
A proper connection between wall versus diaphragm as well as wall versus foundation to
complete the load path
Proper bonding at construction joint in the form of shear friction reinforcement
Provision of diagonal steel in the coupling beam
Fig ndash 1147 Diagonal tension in the form of X shaped
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(v) Infill Walls
Infill panels in reinforced concrete frames are the cause of unequal distribution of lateral forces
in the different frames of a building producing vertical and horizontal irregularities etc the
common mode of failure of infill masonry are in plane or shear failure
Mode ndash 9 Shear failure of masonry infill
Mechanism Frame with infill possesses much more lateral stiffness than the bare frame and
hence initially attracts most of the lateral force during an earthquake Being brittle the infill
starts to disintegrate as soon as its strength is reached Infills that were not adequately tied to the
surrounding frames sometimes dislodges by out-of-plane seismic excitations
Reasons Infill causes asymmetry of load application resulting in increased torsional forces and
changes in the distribution of shear forces between lateral load resisting system
Remedies Two strategies are possible either complete separation between infill walls and frame
by providing separation joint so that the two systems do not interact or complete anchoring
between frame and infill to act as an integral unit Horizontal and vertical reinforcement may also
be used to improve the strength stiffness and deformability of masonry infill walls
(vi) Parapets
Un-reinforced concrete parapets with large height-to-thickness ratio and not in proper anchoring
to the roof diaphragm may also constitute a hazard The hazard posed by a parapet increases in
direct proportion to its height above building base which has been generally observed
The common mode of failure of parapet wall is against out-of-plane forces which is described as
follows
Mode ndash 10 Brittle flexure out-of-plane failure
Mechanism Parapet walls are acceleration sensitive in the out-of-plane direction the result is
that they may become disengaged and topple
Fig ndash 1148 Shear failure of masonry infill
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Reasons Not properly braced
Remedies Analysed for acceleration forces and braced and connected with roof diaphragm
114 चचनमई सरचनमओ की रटरोफिट ग Retrofitting of Masonry Structures
(a) Principle of Seismic Safety of Masonry Buildings
Integral box action
Integrity of various components
- Roof to wall
- Wall to wall at corners
- Wall to foundation
Limit on openings
(b) Methods for Retrofitting of Masonry Buildings
Repairing (Improving existing masonry strength)
Stitching of cracks
Grouting with cement or epoxy
Use of CFRP (Carbon Fibre Reinforced Polymer) strips
Fig ndash 1149 Brittle flexure out-of-plane failure
(a) (b)
Fig ndash 1150 (a) Stitching of cracks Fig ndash 1150 (b) Repair of damaged member in
masonry walls
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(c) Retrofitting of Earthquake vulnerable buildings
External binding or jacketing
Shotcreting
Strengthening of wall intersections
Strengthening by cross wall
Strengthening by buttresses
Strengthening of arches
Fig ndash 1151 Integral Box action
(a) (b)
Fig - 1152 (a) Strengthening of Wall Fig - 1152 (b) Strengthening by
intersections cross wall
(a) (b)
Fig ndash 1153 (a) Strengthening by Fig ndash 1153 (b) Strengthening of Arches
Buttresses
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143
पररलिष Annexure ndash I
भारिीय भको पी सोतििाएा Indian Seismic Codes
Development of building codes in India started rather early Today India has a fairly good range
of seismic codes covering a variety of structures ranging from mud or low strength masonry
houses to modern buildings However the key to ensuring earthquake safety lies in having a
robust mechanism that enforces and implements these design code provisions in actual
constructions
भको पी तिजाइन कोि का मितव Importance of Seismic Design Codes
Ground vibrations during earthquakes cause forces and deformations in structures Structures
need to be designed to withstand such forces and deformations Seismic codes help to improve
the behaviour of structures so that they may withstand the earthquake effects without significant
loss of life and property An earthquake-resistant building has four virtues in it namely
(a) Good Structural Configuration Its size shape and structural system carrying loads are such
that they ensure a direct and smooth flow of inertia forces to the ground
(b) Lateral Strength The maximum lateral (horizontal) force that it can resist is such that the
damage induced in it does not result in collapse
(c) Adequate Stiffness Its lateral load resisting system is such that the earthquake-induced
deformations in it do not damage its contents under low-to moderate shaking
(d) Good Ductility Its capacity to undergo large deformations under severe earthquake shaking
even after yielding is improved by favourable design and detailing strategies
Seismic codes cover all these aspects
भारिीय भको पी सोतििाएा Indian Seismic Codes
Seismic codes are unique to a particular region or country They take into account the local
seismology accepted level of seismic risk building typologies and materials and methods used
in construction The first formal seismic code in India namely IS 1893 was published in 1962
Today the Bureau of Indian Standards (BIS) has the following seismic codes
1 IS 1893 (Part I) 2002 Indian Standard Criteria for Earthquake Resistant Design of
Structures (5 Revision)
2 IS 4326 1993 Indian Standard Code of Practice for Earthquake Resistant Design and
Construction of Buildings (2nd Revision)
3 IS 13827 1993 Indian Standard Guidelines for Improving Earthquake Resistance of
Earthen Buildings
4 IS 13828 1993 Indian Standard Guidelines for Improving Earthquake Resistance of Low
Strength Masonry Buildings
5 IS 13920 1993 Indian Standard Code of Practice for Ductile Detailing of Reinforced
Concrete Structures Subjected to Seismic Forces
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6 IS 13935 1993 Indian Standard Guidelines for Repair and Seismic Strengthening of
Buildings
The regulations in these standards do not ensure that structures suffer no damage during
earthquake of all magnitudes But to the extent possible they ensure that structures are able to
respond to earthquake shakings of moderate intensities without structural damage and of heavy
intensities without total collapse
IS 1893 (Part I) 2002
IS 1893 is the main code that provides the seismic zone map and specifies seismic design force
This force depends on the mass and seismic coefficient of the structure the latter in turn
depends on properties like seismic zone in which structure lies importance of the structure its
stiffness the soil on which it rests and its ductility For example a building in Bhuj will have
225 times the seismic design force of an identical building in Bombay Similarly the seismic
coefficient for a single-storey building may have 25 times that of a 15-storey building
The revised 2002 edition Part 1 of IS1893 contains provisions that are general in nature and
those applicable for buildings The other four parts of IS 1893 will cover
a) Liquid-Retaining Tanks both elevated and ground supported (Part 2)
b) Bridges and Retaining Walls (Part 3)
c) Industrial Structures including Stack Like Structures (Part 4) and
d) Dams and Embankments (Part 5)
These four documents are under preparation In contrast the 1984 edition of IS1893 had
provisions for all the above structures in a single document
Provisions for Bridges
Seismic design of bridges in India is covered in three codes namely IS 1893 (1984) from the
BIS IRC 6 (2000) from the Indian Roads Congress and Bridge Rules (1964) from the Ministry
of Railways All highway bridges are required to comply with IRC 6 and all railway bridges
with Bridge Rules These three codes are conceptually the same even though there are some
differences in their implementation After the 2001 Bhuj earthquake in 2002 the IRC released
interim provisions that make significant improvements to the IRC6 (2000) seismic provisions
IS 4326 1993 (Reaffirmed 2003)
This code covers general principles for earthquake resistant buildings Selection of materials
and special features of design and construction are dealt with for the following types of
buildings timber constructions masonry constructions using rectangular masonry units and
buildings with prefabricated reinforced concrete roofingflooring elements The code
incorporates Amendment No 3 (January 2005)
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IS 13827 1993 and IS 13828 1993
Guidelines in IS 13827 deal with empirical design and construction aspects for improving
earthquake resistance of earthen houses and those in IS 13828 with general principles of
design and special construction features for improving earthquake resistance of buildings of
low-strength masonry This Masonry includes burnt clay brick or stone masonry in weak
mortars like clay-mud These standards are applicable in seismic zones III IV and V
Constructions based on them are termed non-engineered and are not totally free from collapse
under seismic shaking intensities VIII (MMI) and higher Inclusion of features mentioned in
these guidelines may only enhance the seismic resistance and reduce chances of collapse
IS 13920 1993 (Reaffirmed 2003)
In India reinforced concrete structures are designed and detailed as per the Indian Code IS 456
(2002) However structures located in high seismic regions require ductile design and
detailing Provisions for the ductile detailing of monolithic reinforced concrete frame and shear
wall structures are specified in IS 13920 (1993) After the 2001 Bhuj earthquake this code has
been made mandatory for all structures in zones III IV and V Similar provisions for seismic
design and ductile detailing of steel structures are not yet available in the Indian codes
IS 13935 1993
These guidelines cover general principles of seismic strengthening selection of materials and
techniques for repairseismic strengthening of masonry and wooden buildings The code
provides a brief coverage for individual reinforced concrete members in such buildings but
does not cover reinforced concrete frame or shear wall buildings as a whole Some guidelines
are also laid down for non-structural and architectural components of buildings
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पररलिष Annexure ndash II
Checklist Multiple Choice Questions for Points to be kept in mind during
Construction of Earthquake Resistant Building
S No Description Observer Remarks
1 Seismic Zone in which building is located
i) Zone II ndash Least Seismically Prone Region
ii) Zone III ndash
iii) Zone IV ndash
iv) Zone V ndash Most Seismically Prone Region
Choose Zone
2 Environment condition to which building is exposed
a) Mild b) Moderate c) Severe d) Very Severe e) Extreme
Choose Condition
3 Whether the building is located in Flood Zone YesNo
4 Whether the building is located in Land Slide Zone ie building is on
hill slope or Plane Area
YesNo
5 Type of soil at founding level
a) Rock or Hard Soil
b) Medium Soil
c) Soft Soil
Choose type of soil
6 Type of Building
I) Load Bearing Masonry Building
a) Brick Masonry Construction
b) Stone Masonry construction
II) RCC Framed Structure
a) Regular frame
b) Regular Frame with shear wall
c) Irregular Frame
d) Irregular Frame with shear wall
e) Soft Story Building
Choose type of
building
7 No of Story above Ground Level with provision of Future Extension Mention Storey
8 Category of Building considering Seismic Zone and Importance
Factor (As per Table ndash 102)
i) Category B ndash Building in Seismic Zone II with Importance Factor
10
ii) Category E- Building in Seismic Zone II with Importance Factor
10 and 150
Choose category
9 Bricks should not have compressive strength less than 350 MPa YesNo
10 Minimum wall thickness of brick masonry
i) 1 Brick ndash Single Storey Construction
ii) 1 frac12 Brick ndash In bottom storey up to 3 storey construction amp
1 Brick in top storey with brick masonry
Choose appropriate
11 Height of building is restricted to
i) For A B amp C categories ndash G+2 with flat roof G+1 plus anti for
pitched roof when height of each story not exceed 3 m
ii) D category ndash G+1 with flat Roof
- Ground plus attic for pitched roof
Choose appropriate
12 Max Height of Brick masonry Building ndash 15 m (max 4 storey) YesNo
13 Mortar mix shall be as per Table ndash 102 for category A to E Choose Mortar
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14 Height of Stone Masonry wall
i) For Categories AampB ndash
a) When built in Lime-Sand or Mud mortar
ndash Two storey with flat roof or One Storey plus attic
b) When build in cement sand 16 mortar
- One story higher
ii) For Categories CampD ndash
a) When built in cement Sand 16 Mortar
- Two storey with flat roof or One Storey plus attic for pitched
roof
b) When build in lime sand or Mud mortar
- One story with flat roof or One Story plus attic
Choose appropriate
15 Through stone at full length equal to wall thickness in every 600 mm
lift at not more than 120 m apart horizontally has been provided
YesNo
16 Through stone and Bond Element as per Fig 1024 has been provided YesNo
17 Horizontal Bands
a) Plinth Band
b) Lintel Band
c) Roof Bond
d) Gable Bond
For Over Strengthening Arrangement for Category D amp E Building
have been provided
YesNo
18 Bond shall be made up of Reinforced Concrete of Grade not leaner
than M15 or Reinforced brick work in cement mortar not leaner than
13
YesNo
19 Bond shall be of full width of wall not less than 75 mm in depth and
reinforced with steel as shown in Table ndash 106
YesNo
20 Vertical steel at corners amp junction of wall which are up to 340 mm
(1 frac12 brick) thick shall be provided as shown in Table ndash 101
YesNo
21 General principal for planning building are
i) Building should be as light as possible
ii) All parts of building should be tied together to act as one unit
iii) Projecting part should be avoided
iv) Building having plans with shape L T E and Y shall preferably
be separated in to rectangular parts
v) Structure not to be founded on loose soil which will subside or
liquefy during Earthquake resulting in large differential
settlement
vi) Heavy roofing material should be avoided
vii) Large stair hall shall be separated from Rest of the Building by
means of separation or crumple section
viii) All of the above
ix) None of the above
Choose Correct
22 Structural irregularities may be
i) Horizontal Irregularities
ii) Vertical Irregularities
iii) All of the above
iv) None of the above
Choose Correct
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23 Horizontal Irregularities are
i) Asymmetrical plan shape (eg LTUF)
ii) Horizontal resisting elements (diaphragms)
iii) All of the above
iv) None of the above
Choose Correct
24 Horizontal Irregularities result in
i) Torsion
ii) Diaphragm deformation
iii) Stress Concentration
iv) All of the above
v) None of the above
Choose Correct
25 Vertical Irregularities are
i) Sudden change of stiffness over height of building
ii) Sudden change of strength over height of building
iii) Sudden change of geometry over height of building
iv) Sudden change of mass over height of building
v) All of the above
vi) None of the above
Choose Correct
26 Soft story in one
i) Which has lateral stiffness lt 70 of story above
ii) Which has lateral stiffness lt 80 of average lateral stiffness of 3
storeys above
iii)All of the above
vi) None of the above
Choose Correct
27 Extreme soft storey in one
i) Which has lateral stiffness lt 60 of storey above
ii) Which has lateral stiffness lt 70 of average lateral stiffness of 3
storeys above
iii)All of the above
iv)None of the above
Choose Correct
28 Weak Storey is one
i) Which has lateral strength lt 80 of storey above
ii) Which has lateral strength lt 80 of storey above
iii)All of the above
iv)None of the above
Choose Correct
29 Natural Period of Building
It is the time taken by the building to undergo one complete
cycle of oscillation during shaking
True False
30 Fundamental Natural Period of Building
Natural period with smallest Natural Frequency ie with largest
natural period is called Fundamental Natural Period
True False
31
Type of building frame system
i) Ordinary RC Moment Resisting Frame (OMRF)
ii) Special RC Moment Resisting Frame (SMRF)
iii) Ordinary Shear Wall with OMRF
iv) Ordinary Shear Wall with SMRF
v) Ductile Shear wall with OMRF
vi) Ductile Shear wall with SMRF
vii) All of the above
Choose Correct
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32 Zone factor to be considered for
i) Zone II ndash 010
ii) Zone III ndash 016
iii) Zone IV ndash 024
iv) Zone V ndash 036
True False
33 Importance Factor
i) Important building like school hospital railway station 15
ii) All other buildings 10
True False
34 Design of Earthquake effect is termed as
i) Earthquake Proof Design
or
ii) Earthquake Resistant Design
Choose Correct
35 Seismic Analysis is carried out by
i) Dynamic analysis procedure [Clause 78 of IS1893 (Part I) 2002]
ii) Simplified method referred as Lateral Force Procedure [Clause
75 of IS 1893 (Part I) 2002]
True False
36 Dynamic Analysis is performed for following buildings
(a) Regular Building gt 40 m height in Zone IV amp V
gt 90 height in Zone II amp III
(b) Irregular Building
gt 12 m all framed building in Zone IV amp V
gt 40 m all framed building in Zone II and III
True False
37 Base Shear for Lateral Force Procedure is
VB = Ah W =
True False
38 Distribution of Base Shear to different Floor level is
True False
39 Concept of capacity design is to
Ensure that brittle element will remain elastic at all loads prior to
failure of ductile element
True False
40 lsquoStrong Column ndash Weak Beamrsquo Philosophy is
For a building to remain safe during Earthquake shacking columns
should be stronger than beams and foundation should be stronger
than columns
True False
41 Rigid Diaphragm Action is
Geometric distortion of Slab in horizontal plane under influence of
horizontal Earthquake force is negligible This behaviour is known
as Rigid Diaphragm Action
True False
42 Soft storied buildings are
Column on Ground Storey do not have infill walls (of either
masonry or RC)
True False
43 Soft Storey or Open Ground Story is also termed as weak storey True False
44 Short columns in building suffer significant damage during an earth-
quake
True False
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45 Building can be protected from damage due to Earthquake effect by
using
a) Base Isolation Devices
b) Seismic Dampers
True False
46 Idea behind Base Isolation is
To detach building from Ground so that EQ motion are not
transmitted through the building or at least greatly reduced
True False
47 Base Isolation is done through
Flexible Pads connected to building and foundation True False
48 Seismic Dampers are
(i) Special devices to absorb the energy provided by Ground Motion
to the building
(ii) They act like hydraulic shock absorber in cars
True False
49 Commonly used Seismic Dampers are
(i) Viscous Dampers
(ii) Friction Dampers
(iii) Yielding Dampers
True False
50 For Ductility Requirement
(i) Min Grade of Concrete shall be M20 for all buildings having
more than 3 storeys in height
(ii) Steel Reinforcement of Grade Fe 415 or less only shall be used
(iii) Grade Fe 500 amp Fe 550 having elongation more than 145 may
be used
True False
51 For Ductility Requirement Flexure Members shall satisfy the
following requirement
(i) width of member shall not be less than 200 mm
(ii) width to depth ratio gt 03
(iii) depth of member D lt 14th of clear span
(iv) Factored Axial Stress on the member under Earthquake loading
shall not be greater than 01 fck
True False
52 For Ductility Requirement Longitudinal reinforcement in Flexure
Member shall satisfy the following requirements
i) Top and bottom reinforcement consist of at least 2 bars
throughout member length
ii) Tensile Steel Ratio on any face at any section shall not be less
than ρmin = (024 radic fck) fy
iii) Max Steel ratio on any face at any section shall not exceed
ρmax = 0025
iv) + ve steel at Joint face must be at least equal to half the ndashve steel
at that face
v) Steel provided at each of the top amp bottom face of the member
at any section along its length shall be at least equal to 14th of
max ndashve moment steel provided at the face of either joint
True False
कमटक2017नसईआरबी10
CAMTECH2017CERB10
भकमप परनतरसिी भवि निमााण मई ndash 2017 CONSTRUCTION OF EARTHQUAKE RESISTANT BUILDING May ndash 2017
151
(vi) Detailing of Reinforcement at Beam-Column Joint
(vii) Detailing of Splicing
53 For Ductile Requirement in compression member
i) Minimum diversion of member shall not be less than 200 mm
ii) In Frames with beams cc Span gt 5m or
unsupported length of column gt 4 m shortest dimension shall not
be less than 300 mm
iii) Ratio of shortest cross sectional dimension to the perpendicular
dimension shall probably not less than 04
True False
54 For Ductile Requirement Longitudinal reinforcement in compression
member shall satisfy the following requirements
i) Lap splice shall be provided only in the central half of the member
length proportional as tension splice
ii) Hoop shall be provided over entire splice length at spacing not
greater than 150 mm
iii) Not more than 50 bar shall be spliced at one section
True False
55 When a column terminates into a footing or mat special confining
reinforcement shall extend at least 300 mm into the footing or mat
True False
कमटक2017नसईआरबी10
CAMTECH2017CERB10
भकमप परनतरसिी भवि निमााण मई ndash 2017 CONSTRUCTION OF EARTHQUAKE RESISTANT BUILDING May ndash 2017
152
सोदभयगरोथ सची BIBLIOGRAPHY
1 Guidelines for Earthquake Resistant Non-Engineered Construction reprinted by
Indian Institute of Technology Kanpur 208016 India (Source wwwniceeorg)
2 IS 1893 (Part 1) 2002 Criteria for Earthquake Resistant Design Of Structures
PART- 1 GENERAL PROVISIONS AND BUILDINGS (Fifth Revision )
3
IS 4326 1993 (Reaffirmed 1998) Edition 32 (2002-04) Earthquake Resistant
Design and Construction of Buildings ndash Code of Practice ( Second Revision )
(Incorporating Amendment Nos 1 amp 2)
4 IS 13828 1993 (Reaffirmed 1998) Improving Earthquake Resistance of Low
Strength Masonry Buildings ndash Guidelines
5
IS 13920 1993 (Reaffirmed 1998) Edition 12 (2002-03) Ductile Detailing of
Reinforced Concrete Structures subjected to Seismic Forces ndash Code of Practice
(Incorporating Amendment Nos 1 amp 2)
6 IS 13935 1993 (Reaffirmed 1998) Edition 11 (2002-04) Repair and Seismic
Strengthening of Buildings ndash Guidelines (Incorporating Amendment No 1)
7
Earthquake Tips authored by Prof C V R Murty IIT Kanpur and sponsored by
Building Materials and Technology Promotion Council New Delhi India
(Source www wwwiitkacin)
8
Earthquake Engineering Practice Volume 1 Issue 1 March 2007 published by
National Information Center of Earthquake Engineering IIT Kanpur Kanpur
208016
9 Earthquake Resistant Design of Structures by Pankaj Agarwal and Manish
Shrikhande published by PHI Learning Private Limited Delhi 110092 (2015)
कमटक2017नसईआरबी10
CAMTECH2017CERB10
भकमप परनतरसिी भवि निमााण मई ndash 2017 CONSTRUCTION OF EARTHQUAKE RESISTANT BUILDING May ndash 2017
153
तटपपणी NOTES
कमटक2017नसईआरबी10
CAMTECH2017CERB10
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154
तटपपणी NOTES
कमटक2017नसईआरबी10
CAMTECH2017CERB10
भकमप परनतरसिी भवि निमााण मई ndash 2017 CONSTRUCTION OF EARTHQUAKE RESISTANT BUILDING May ndash 2017
155
हमारा उददशय
अनरकषि परौधौधगकी और कायापरिाली को उननयन करना तथा उतपादकता और
रलव की पररसमपवियो एव िनशजतत क ननषपादन म सधार करना जिसस
अतववाियो म ववशवसनीयता उपयोधगता और दकषता परापत की िा सकA
Our Objective
To upgrade Maintenance Technologies and Methodologies and achieve
improvement in productivity and performance of all Railway assets and
manpower which inter-alia would cover Reliability Availability and
Utilisation
तिसलमर Disclaimer
The document prepared by CAMTECH is meant for the dissemination of the knowledge information
mentioned herein to the field staff of Indian Railways The contents of this handbookbooklet are only for
guidance Most of the data amp information contained herein in the form of numerical values are indicative
and based on codes and teststrials conducted by various agencies generally believed to be reliable While
reasonable care and effort has been taken to ensure that information given is at the time believed to be fare
and correct and opinion based thereupon are reasonable Due to very nature of research it can not be
represented that it is accurate or complete and it should not be relied upon as such The readeruser is
supposed to refer the relevant codes manuals available on the subject before actual implementation in the
field
कमटक2017नसईआरबी10
CAMTECH2017CERB10
भकमप परनतरसिी भवि निमााण मई ndash 2017 CONSTRUCTION OF EARTHQUAKE RESISTANT BUILDING May ndash 2017
156
Hkkjrh jsy jkrdquoV ordf dh thou js[kk ---hellip
INDIAN RAILWAYS Lifeline to the nation hellip
If you have any suggestion amp comments please write to us
Contact person Joint Director (Civil)
Phone (0751) - 2470869
Fax (0751) ndash 2470841
Email dircivilcamtechgmailcom
Charbagh Railway Station Lucknow
भतमका
भारतीय रलव एक बड़ा सगठन ह जिसक पास ससववल इिीननयररग सरचनाओ एव भवनो की ववशाल सपदा मौिद ह भकप की ववनाशकारी परकनत को धयान म रखत हए यह आवशयक ह कक लगभग सभी भवनो चाह व आवासीय ससथागत शकषणिक इतयादद क हो उनकी योिना डििाइन ननमााि तथा रखरखाव भकप परनतरोधी तरीको को अपनाकर ककया िाना चादहए जिसस कक भकप क कारि मानव िीवन व सपवि क नकसान को नयनतम ककया िा सक
ldquoभकप परतिरोधी भवनो क तनरमाणrdquo पर यह हसतपजसतका एक िगह पर पयाापत सामगरी परदान करन का एक परयास ह ताकक वयजतत भवनो क भकप परनतरोधी ननमााि क सलए मलभत ससदधातो को ववकससत कर सही तथा वयवहाररक कायाववधध को अमल म ला सक
इस हसतपजसतका की सामगरी को गयारह अधयायो म ववभाजित ककया गया ह अधयमय-1 पररचय तथा अधयमय-2 भकप इिीननयररग म परयतत शबदावली पररभावित करता ह अधयमय-3 भकप व भकपी खतरो क बार म बननयादी जञान को सकषप म वणिात करता ह अधयमय- 4 भकप पररमाि तथा तीवरता क माप क साथ भारत क भकपीय ज़ोन मानधचतर भकप की ननगरानी क सलए एिससयो क बार म िानकारी परदान करता ह अधयमय-5 व 6 भवन लआउट म भकप परनतरोध क सधार क सलए वयापक ससदधात को बताता ह अधयमय-7 भवन की गनतशील परनतकिया को दशााता ह अधयमय-8 और 9 म कोि पर आधाररत पाशवा बल ननधाारि का तरीका तथा बहमजिला भवन की ldquoितटाइल डिटसलग तथा कपससटी डििाइनrdquo को धयान म रखत हए डििाइन का उदाहरि परसतत ककया गया ह अधयमय-10 म कम शजतत की धचनाई दवारा सरचनाओ क ननमााि को भकप परनतरोधी ससदधातो को धयान म रख वणिात ककया गया ह अधयमय -11 म मौिदा भवनो की भकप परनतरोधी आवशयकताओ को परा करन क सलए भवनो क मौिदा भकपरोधी मलयाकन और पनः सयोिन पर परकाश िाला गया ह
यह हसतपजसतका मखयतः भारतीय रल क फीलि तथा डििाइन कायाालय म कायारत िईएसएसई सतर क सलए ह इस हसतपजसतका को भारतीय रल क ससववल इिीननयसा तथा अनय ववभागो क इिीननयसा दवारा एक सदभा पजसतका क रप म भी इसतमाल ककया िा सकता ह
म शरी एस क ठतकर परोफसर (ररटायिा) आई आई टी रड़की को उनक दवारा ददय गए मागादशान तथा सझावो क सलए अतयनत आभारी ह तथा शरी क सी शातय एसएसईससववल को इस हसतपजसतका क सकलन म उनक समवपात सहयोग क सलए धनयवाद दता ह
यदयवप इस हसतपजसतका को तयार करन म हर तरह की सावधानी बरती गई ह कफर भी कोई तरदट या चक हो तो कपया IRCAMTECHGwalior की िानकारी म लायी िा सकती ह
भारतीय रल क सभी अधधकाररयो और इकाइयो दवारा पसतक की सामगरी म ववसतार तथा सधार क सलए ददय िान वाल सझावो का सवागत ह
कमटक गवातलयर (िी क गपता) 23 मई 2017 सोयकत तनदशकतसतवल
PREFACE
Indian Railways is a big organisation having large assets of Civil Engineering Structures
and Buildings Keeping in mind the destructive nature of Earthquake it is essential that
almost all buildings whether residential institutional educational assembly etc should
be planned designed constructed as well as maintained by adopting Earthquake
Resistant features so that loss due to earthquake to human lives and properties can be
minimised
This handbook on ldquoConstruction of Earthquake Resistant Buildingsrdquo is an attempt to
provide enough material at one place for individual to develop the basic concept for
correctly interpreting and using practices for earthquake resistant construction of
Buildings
Content of this handbook is divided into Eleven Chapters Chapter-1 is Introduction
and Chapter-2 defines Terminology frequently used in Earthquake Engineering
Chapter-3 describes in brief Basic knowledge about Earthquake amp Seismic Hazards
Chapter-4 deals with Measurement of Earthquake magnitude amp intensity with
information about Seismic Zoning Map of India and Agencies for Earthquake
monitoring Chapter-5 amp 6 elaborates General Principle for improving Earthquake
resistance in building layouts Chapter-7 features Dynamic Response of Building In
Chapter-8 amp 9 Codal based procedure for determining lateral loads and Design of
multi-storeyed building with solved example considering Ductile Detailing and Capacity
Design Concept is covered Chapter-10 describes Construction of Low strength
Masonry Structure considering earthquake resistant aspect Chapter-11 enlighten
ldquoSeismic Evaluation amp Retrofittingrdquo for structural upgrading of existing buildings to
meet the seismic requirements
This handbook is primarily written for JESSE level over Indian Railways working in
Field and Design office This handbook can also be used as a reference book by Civil
Engineers and Engineers of other departments of Indian Railways
I sincerely acknowledge the valuable guidance amp suggestion by Shri SK Thakkar
Professor (Retd) IIT Roorkee and also thankful to Shri KC Shakya SSECivil for his
dedicated cooperation in compilation of this handbook
Though every care has been taken in preparing this handbook any error or omission
may please be brought out to the notice of IRCAMTECHGwalior
Suggestion for addition and improvement in the contents from all officers amp units of
Indian Railways are most welcome
CAMTECHGwalior (DK Gupta)
23 May 2017 Joint DirectorCivil
तवषय-सची CONTENT
अधयाय CHAPTER
तववरण DESCRIPTION
पषठ
सोPAGE
NO
पराककथन FOREWORD FROM MEMBER ENGINEERING RLY BOARD पराककथन FOREWORD FROM ADG RDSO पराककथन FOREWORD FROM ED CAMTECH भतमका PREFACE
तवषय-सची CONTENT
सोशोधन पतचययाो CORRECTION SLIPS
1 पररचय Introduction 01
2 भको प इोजीतनयररोग क तलए शबदावली Terminology for Earthquake
Engineering 02-05
3 भको प क बार म About Earthquake 06-16
31 भको प Earthquake 06
32 नकि कारणसो स िसता ि भको प What causes Earthquake 06
33 नववतानिक गनतनवनि Tectonic Activity 06
34 नववतानिक पलट का नसदाोत Theory of Plate Tectonics 07
35 लचीला ररबाउोड नसदाोत Elastic Rebound Theory 11
36 भको प और दसष क परकार Types of Earthquakes and Faults 11
37 जमीि कस निलती ि How the Ground shakes 12
38 भको प या भको पी खतरसो का परभाव Effects of Earthquake or Seismic
Hazards 13
4 भको पी जोन और भको प का मापन Seismic Zone and Measurement
of Earthquake 17-28
41 भको पी जसि Seismic Zone 17
42 भको प का मापि Measurement of Earthquake 19
43 भको प पररमाण सकल क परकार Types of Earthquake Magnitude
Scales 20
44 भको प तीवरता Earthquake Intensity 22
45 भको प निगरािी और सवाओो क नलए एजनसयसो Agencies for Earthquake
Monitoring and Services 28
5 भवन म भको प परतिरोध म सधार क तलए सामानय तसदाोि General
Principle for improving Earthquake Resistance in Building 29-33
51 िलकापि Lightness 29
52 निमााण की निरोतरता Continuity of Construction 29
53 परसजसतटोग एवो ससपडड पाटटास Projecting and Suspended Parts 29
54 भवि की आकनत Shape of Building 29
55 सनविा जिक नबसतडोग लआउट Preferred Building Layouts 30
56 नवनभनन नदशाओो म शसति Strength in Various Directions 30
57 िी ोव Foundations 30
58 छत एवो मोनजल Roofs and Floors 30
59 सीनियाो Staircases 31
510 बॉकस परकार निमााण Box Type Construction 33
511 अनि सरिा Fire Safety 33
6
भको प क दौरान आर सी भवनो ो क परदशयन पर सटरकचरल अतनयतमििाओो
का परभाव Effect of Structural Irregularities on Performance of
RC Buildings during Earthquakes
34-38
61 सटर कचरल अनियनमतताओो का परभाव Effect of Structural Irregularities 34
62 िनतज अनियनमतताएो Horizontal Irregularities 34
63 ऊरधाािर अनियनमतताएो Vertical Irregularities 36
64
भवि नवनयास अनियनमतताएो ndash समसयाए ववशलिि एव ननदान क उपाय Building Irregularities ndash Problems Analysis and Remedial
Measures 37
7 भवन की िायनातमक तवशषिाएा Dynamic Characteristics of
Building 39-47
71 डायिानमक नवशषताए Dynamic Characteristics 39
72 पराकनतक अवनि Natural Period 39
73 पराकनतक आवनि Natural Frequency 39
74 पराकनतक अवनि कस परभानवत करि वाल कारक Factors influencing
Natural Period 40
75 Mode आकनत Mode Shape 42
76 Mode आकनतयसो कस परभानवत करि वाल कारक Factors influencing
Mode Shapes 44
77 सोरचिा की परनतनकरया Response of Structure 46
78 नडजाइि सपटर म Design Spectrum 46
8 तिजाइन पारशय बलो ो क तनधायरण क तलए कोि आधाररि िरीका Code
Based Procedure for Determination of Design Lateral Loads 48-59
81 भको पी नडजाइि की नफलससफ़ी Philosophy of Seismic Design 48
82 भको पी नवशलषण क नलए तरीक Methods for Seismic Analysis 48
83 डायिानमक नवशलषण Dynamic Analysis 49
84 पारशा बल परनकरया Lateral Force Procedure 49
85 को पि की मौनलक पराकनतक अवनि Fundamental Natural Period of
Vibration 52
86 नडजाइि पारशा बल Design Lateral Force 53
87 नडजाइि बल का नवतरण Distribution of Design Force 53
88 नडजाइि उदािरण Design Example ndash To determine Base Shear and
its distribution along Height of Building 54
9 ढााचागि सोरचना का तनमायण Construction of Framed Structure 60-90
91
गरतवाकषाण लसनडोग और भको प लसनडोग म आर सी नबसतडोग का वयविार Behaviour of RC Building in Gravity Loading and Earthquake
Loading 60
92 परबनलत को करीट इमारतसो पर िनतज भको प का परभाव Effect of Horizontal
Earthquake Force on RC Buildings 61
93 िमता नडजाइि सोकलपिा Capacity Design Concept 61
94 लचीलापि और ऊजाा का अपवयय Ductility and Energy Dissipation 62
95 lsquoमजबतिोभ ndash कमजसर बीमrsquo फलससफ़ी lsquoStrong Column ndash Weak
Beamrsquo Philosophy 62
96 कठसर डायाफराम नकरया Rigid Diaphragm Action 63
97
सॉफट सटसरी नबसतडोग क साथ ndash ओपि गराउोड सटसरी नबसतडोग जस नक भको प क
समय कमजसर िसती ि Building with Soft storey ndash Open Ground
Storey Building that is vulnerable in Earthquake 63
98 भको प क दौराि लघ कॉलम वाली इमारतसो का वयविार Behavior of
Buildings with Short Columns during Earthquakes 65
99 भको प परनतरसिी इमारतसो की लचीलापि आवशयकताए Ductility
requirements of Earthquake Resistant Buildings 66
910
बीम नजनह आर सी इमारतसो म भको प बलसो का नवरसि करि क नलए डाला जाता
ि Beams that are required to resist Earthquake Forces in RC
Buildings 66
911 फलकसचरल ममबसा क नलए सामानय आवशयकताए General Requirements
for Flexural Members 68
912
कॉलम नजनह आर सी इमारतसो म भको प बलसो का नवरसि करि क नलए डाला
जाता ि Columns that are required to resist Earthquake Forces in
RC Buildings 69
913 एकसीयल लसडड मबसा क नलए सामानय आवशयकताए General
Requirements for Axial Loaded Members 71
914 बीम-कॉलम जसड जस आर सी भविसो म भको प बलसो का नवरसि करत ि Beam-
Column Joints that resist Earthquakes Forces in RC Buildings 72
915 नवशष सीनमत सदढीकरण Special Confining Reinforcement 74
916
नवशषतः भको पीय ितर म कतरिी दीवारसो वाली इमारतसो का निमााण Construction of Buildings with Shear Walls preferably in Seismic
Regions 75
917 इमपरवड नडजाइि रणिीनतयाो Improved design strategies 76
918 नडजाइि उदािरण Design Example ndash Beam Design of RC Frame
with Ductile Detailing 78
10 अलप सामरथय तचनाई सोरचनाओो क तनमायण Construction of Low
Strength Masonry Structures 91-106
101 भको प क दौराि ईोट नचिाई की दीवारसो का वयविार Behaviour of
Brick Masonry Walls during Earthquakes 91
102 नचिाई वाली इमारतसो म बॉकस एकशि कस सनिनित कर How to ensure
Box Action in Masonry Buildings 92
103 िनतज बड की भनमका Role of Horizontal Bands 93
104 अिसलोब सदढीकरण Vertical Reinforcement 95
105 दीवारसो म सराखसो का सोरिण Protection of Openings in Walls 96
106
भको प परनतरसिी ईोट नचिाई भवि क निमााण ित सामानय नसदाोत General
Principles for Construction of Earthquake Resistant Brick
Masonry Building
97
107 ओपनिोग का परभाव Influence of Openings 100
108 िारक दीवारसो म ओपनिोग परदाि करि की सामानय आवशयकताए General Requirements of Providing Openings in Bearing Walls
100
109 भको पी सदिीकरण वयवसथा Seismic Strengthening Arrangements 101
1010 भको प क दौराि सटसि नचिाई की दीवारसो का वयविार Behaviour of Stone
Masonry Walls during Earthquakes 104
1011
भकप परनतरोधी सटोन धचनाई क ननमााि हत सामानय ससदधात General
Principles for Construction of Earthquake Resistant Stone
Masonry Building
104
11 भकपीय रलयमकन और रटरोफिट ग Seismic Evaluation and
Retrofitting 107-142
111 भकपीय मलयाकन Seismic Evaluation 107
112 भवनो की रटरोकिदटग Retrofitting of Building 116
113
आरसी भवनो क घटको म सामानय भकपी कषनतया और उनक उपचार Common seismic damage in components of RC
Buildings and their remedies 133
114 धचनाई सरचनाओ की रटरोकिदटग Retrofitting of Masonry
Structures 141
Annex ndash I भारिीय भको पी सोतििाएा Indian Seismic Codes 143-145
Annex ndash II Checklist Multiple Choice Questions for Points to be kept in
mind during Construction of Earthquake Resistant Building 146-151
सोदभयगरोथ सची BIBLIOGRAPHY 152
तटपपणी NOTES 153-154
हमारा उददशय एव डिसकलरर OUR OBJECTIVE AND DISCLAIMER
सोशसिि पनचायसो का परकाशि
ISSUE OF CORRECTION SLIPS
इस ििपसतिका क नलए भनवषय म परकानशत िसि वाली सोशसिि पनचायसो कस निमनािसार सोखाोनकत
नकया जाएगा
The correction slips to be issued in future for this handbook will be numbered as
follows
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CAMTECH2017CERB10CS XX date_________________________
जिा xx सोबसतित सोशसिि पची की करम सोखा ि (01 स परारमभ िसकर आग की ओर)
Where ldquoXXrdquo is the serial number of the concerned correction slip (starting
from 01 onwards)
परकातशि सोशोधन पतचययाा W a
CORRECTION SLIPS ISSUED
करसो Sr No
परकाशन
तदनाोक Date of
issue
सोशोतधि पषठ सोखया िथा मद सोखया Page no and Item No modified
तटपपणी Remarks
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अधयाय Chapter ndash 1
पररचय Introduction
To avoid a great earthquake disaster with its severe consequences special consideration must be
given Engineers in seismic countries have the important responsibility to ensure that the new
construction is earthquake resistant and also they must solve the problem posed by existing weak
structures
Most of the loss of life in past earthquakes has occurred due to the collapse of buildings
constructed with traditional materials like stone brick adobe (kachcha house) and wood which
were not particularly engineered to be earthquake resistant In view of the continued use of such
buildings it is essential to introduce earthquake resistance features in their construction
The problem of earthquake engineering can be divided into two parts first to design new
structures to perform satisfactorily during an earthquake and second to retrofit existing structures
so as to reduce the loss of life during an earthquake Every city in the world has a significant
proportion of existing unsafe buildings which will produce a disaster in the event of a strong
ground shaking Engineers have the responsibility to develop appropriate methods of retrofit
which can be applied when the occasion arises
The design of new building to withstand ground shaking is prime responsibility of engineers and
much progress has been made during the past 40 years Many advances have been made such as
the design of ductile reinforced concrete members Methods of base isolation and methods of
increasing the damping in structures are now being utilized for important buildings both new and
existing Improvements in seismic design are continuing to be made such as permitting safe
inelastic deformations in the event of very strong ground shaking
A problem that the engineer must share with the seismologistgeologist is that of prediction of
future occurrence of earthquake which is not possible in current scenario
Earthquake resistant construction requires seismic considerations at all stages from architectural
planning to structural design to actual constructions and quality control
Problems pertaining to Earthquake engineering in a seismic country cannot be solved in a short
time so engineers must be prepared to continue working to improve public safety during
earthquake In time they must control the performance of structures so that effect of earthquake
does not create panic in society and its after effects are easily restorable
To ensure seismic resistant construction earthquake engineering knowledge needs to spread to a
broad spectrum of professional engineers within the country rather than confining it to a few
organizations or individuals as if it were a super-speciality
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अधयाय Chapter ndash 2
भको प इोजीतनयररोग क तलए शबदावली Terminology for Earthquake Engineering
21 फोकस या िाइपोसटर Focus or Hypocenter
In an earthquake the waves emanate from a finite area
of rocks However the point from which the waves
first emanate or where the fault movement starts is
called the earthquake focus or hypocenter
22 इपीसटर Epicentre
The point on the ground surface just above the focus is called the epicentre
23 सििी फोकस भको प Shallow Focus Earthquake
Shallow focus earthquake occurs where the focus is less than 70 km deep from ground surface
24 इोटरमीतिएट फोकस भको प Intermediate Focus Earthquake
Intermediate focus earthquake occurs where the focus is between 70 km to 300 km deep
25 गिरा फोकस भको प Deep Focus Earthquake
Deep focus earthquake occurs where the depth of focus is more than 300 km
26 इपीसटर दरी Epicentre Distance
Distance between epicentre and recording station in km or in degrees is called epicentre distance
27 पवय क झटक Foreshocks
Fore shocks are smaller earthquakes that precede the main earthquake
28 बाद क झटक Aftershocks
Aftershocks are smaller earthquakes that follow the main earthquake
29 पररमाण Magnitude
The magnitude of earthquake is a number which is a measure of energy released in an
earthquake It is defined as logarithm to the base 10 of the maximum trace amplitude expressed
in microns which the standard short-period torsion seismometer (with a period of 08s
Fig 21Basic terminology
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magnification 2800 and damping nearly critical) would register due to the earthquake at an
epicentral distance of 100 km
210 िीवरिा Intensity
The intensity of an earthquake at a place is a measure of the strength of shaking during the
earthquake and is indicated by a number according to the modified Mercalli Scale or MSK
Scale of seismic intensities
211 पररमाण और िीवरिा क बीच बतनयादी फकय Basic difference between Magnitude and
Intensity
Magnitude of an earthquake is a measure of its size
whereas intensity is an indicator of the severity of
shaking generated at a given location Clearly the
severity of shaking is much higher near the
epicenter than farther away
This can be elaborated by considering the analogy
of an electric bulb Here the size of the bulb (100-
Watt) is like the magnitude of an earthquake (M)
and the illumination (measured in lumens) at a
location like the intensity of shaking at that location
(Fig 22)
212 दरवण Liquefaction
Liquefaction is a state in saturated cohesion-less soil wherein the effective shear strength is
reduced to negligible value for all engineering purpose due to pore pressure caused by vibrations
during an earthquake when they approach the total confining pressure In this condition the soil
tends to behave like a fluid mass
213 तववियतनक लकषण Tectonic Feature
The nature of geological formation of the bedrock in the earthrsquos crust revealing regions
characterized by structural features such as dislocation distortion faults folding thrusts
volcanoes with their age of formation which are directly involved in the earth movement or
quake resulting in the above consequences
214 भको पी दरवयमान Seismic Mass
It is the seismic weight divided by acceleration due to gravity
215 भको पी भार Seismic Weight
It is the total dead load plus appropriate amounts of specified imposed load
Fig 22 Reducing illumination with distance
from an electric bulb
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216 आधार Base
It is the level at which inertia forces generated in the structure are transferred to the foundation
which then transfers these forces to the ground
217 दरवयमान का क दर Centre of Mass
The point through which the resultant of the masses of a system acts is called Centre of Mass
This point corresponds to the centre of gravity of masses of system
218 कठोरिा का क दर Centre of Stiffness
The point through which the resultant of the restoring forces of a system acts is called Centre of
stiffness
219 बॉकस परणाली Box System
Box is a bearing wall structure without a space frame where the horizontal forces are resisted by
the walls acting as shear walls
220 पटटा Band
A reinforced concrete reinforced brick or wooden runner provided horizontally in the walls to tie
them together and to impart horizontal bending strength in them
221 लचीलापन Ductility
Ductility of a structure or its members is the capacity to undergo large inelastic deformations
without significant loss of strength or stiffness
222 किरनी दीवार Shear Wall
Shear wall is a wall that is primarily designed to resist lateral forces in its own plane
223 िनय का बयौरा Ductile Detailing
Ductile Detailing is the preferred choice of location and amount of reinforcement in reinforced
concrete structures to provide adequate ductility In steel structures it is the design of members
and their connections to make them adequate ductile
224 लचीला भको पी तवरण गणाोक Elastic Seismic Acceleration Co-Efficient A
This is the horizontal acceleration value as a fraction of acceleration due to gravity versus
natural period of vibration T that shall be used in design of structures
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225 पराकतिक अवतध Natural Period T
Natural period of a structure is its time period of undamped vibration
a) Fundamental Natural Period Tl It is the highest modal time period of vibration along the
considered direction of earthquake motion
b) Modal Natural Period Tk Modal natural period of mode k is the time period of vibration in
mode k
226 नॉमयल मोि Normal Mode
Mode of vibration at which all the masses in a structure attain maximum values of displacements
and rotations and also pass through equilibrium positions simultaneously
227 ओवरसटरगथ Overstrength
Strength considering all factors that may cause its increase eg steel strength being higher than
the specified characteristic strength effect of strain hardening in steel with large strains and
concrete strength being higher than specified characteristic value
228 ररसाोस कमी कारक Response Reduction Factor R
The factor by which the actual lateral force that would be generated if the structure were to
remain elastic during the most severe shaking that is likely at that site shall be reduced to obtain
the design lateral force
229 ररसाोस सकटर म Response Spectrum
The representation of the maximum response of idealized single degree freedom system having
certain period and damping during that earthquake The maximum response is plotted against the
undamped natural period and for various damping values and can be expressed in terms of
maximum absolute acceleration maximum relative velocity or maximum relative displacement
230 तमटटी परोफ़ाइल फकटर Soil Profile Factor S
A factor used to obtain the elastic acceleration spectrum depending on the soil profile below the
foundation of structure
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अधयाय Chapter ndash 3
भको प क बार म About Earthquake
31 भको प Earthquake
Vibrations of earthrsquos surface caused by waves coming from a source of disturbance inside the
earth are described as earthquakes
Earthquake is a natural phenomenon occurring with all uncertainties
During the earthquake ground motions occur in a random fashion both horizontally and
vertically in all directions radiating from epicentre
These cause structures to vibrate and induce inertia forces on them
32 तकन कारणो ो स िोिा ि भको प What causes Earthquake
Earthquakes may be caused by
Tectonic activity
Volcanic activity
Land-slides and rock-falls
Rock bursting in a mine
Nuclear explosions
33 तववियतनक गतितवतध Tectonic Activity
Tectonic activity pertains to geological formation of the bedrock in the earthrsquos crust characterized
by structural features such as dislocation distortion faults folding thrusts volcanoes directly
involved in the earth movement
As engineers we are interested in earthquakes that are large enough and close enough (to the
structure) to cause concern for structural safety- usually caused by tectonic activity
Earth (Fig 31) consists of following segments ndash
solid inner core (radius ~1290km) that consists of heavy
metals (eg nickel and iron)
liquid outer core(thickness ~2200km)
stiffer mantle(thickness ~2900km) that has ability to flow
and
crust(thickness ~5 to 40km) that consists of light
materials (eg basalts and granites)
At the Core the temperature is estimated to be ~2500degC the
pressure ~4 million atmospheres and density ~135 gmcc
this is in contrast to ~25degC 1 atmosphere and 15 gmcc on the surface of the Earth
Fig 31 Inside the Earth
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Due to prevailing high temperature and pressure gradients between the Crust and the Core the
local convective currents in mantle (Fig 32) are developed These convection currents result in a
circulation of the earthrsquos mass hot molten lava comes out and the cold rock mass goes into the
Earth The mass absorbed eventually melts under high temperature and pressure and becomes a
part of the Mantle only to come out again from another location
Near the bottom of the crust horizontal component currents impose shear stresses on bottom of
crust causing movement of plates on earthrsquos surface The movement causes the plates to move
apart in some places and to converge in others
34 तववियतनक पलट का तसदाोि Theory of Plate Tectonics
Tectonic Plates Basic hypothesis of plate tectonics is that the earthrsquos surface consists of a
number of large intact blocks called plates or tectonic plates and these plates move with respect
to each other due to the convective flows of Mantle material which causes the Crust and some
portion of the Mantle to slide on the hot molten outer core The major plates are shown in
Fig 33
The earthrsquos crust is divided into six continental-sized plates (African American Antarctic
Australia-Indian Eurasian and Pacific) and about 14 of sub-continental size (eg Carribean
Cocos Nazca Philippine etc) Smaller platelets or micro-plates also have broken off from the
larger plates in the vicinity of many of the major plate boundaries
Fig 32 Convention current in mantle
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Fig 33 The major tectonic plates mid-oceanic ridges trenches and transform faults of
the earth Arrows indicate the directions of plate movement
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The relative deformation between plates occurs only in narrow zones near their boundaries
These deformations are
1 Aseismic deformation This deformation of the plates occurs slowly and continuously
2 Seismic deformation This deformation occurs with sudden outburst of energy in the form of
earthquakes
The boundaries are (i) Convergent (ii) Divergent (iii) Transform
Convergent boundary Sometimes the plate in the front is slower Then the plate behind it
comes and collides (and mountains are formed) This type of inter-plate interaction is the
convergent boundary (Fig 34)
Divergent boundary Sometimes two plates move away from one another (and rifts are
created) This type of inter-plate interaction is the divergent boundary (Fig 35)
Transform boundary Sometimes two plates move side-by-side along the same direction or in
opposite directions This type of inter-plate interaction is the transform boundary (Fig 36)
Since the deformation occurs predominantly at the boundaries between the plates it would be
expected that the locations of earthquakes would be concentrated near plate boundaries The map
of earthquake epicentres shown in Fig 37 provides strong support to confirm the theory of plate
tectonics The dots represent the epicentres of significant earthquakes It is apparent that the
locations of the great majority of earthquakes correspond to the boundaries between plates
Fig 34 Convergent Boundary
Fig 35 Divergent Boundary
Fig 36 Transform Boundary
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Fig 37 Worldwide seismic activity
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35 लचीला ररबाउोि तसदाोि Elastic Rebound Theory
Earth crust for some reason is moving in opposite
directions on certain faults This sets up elastic
strains in the rocks in the region near this fault As
the motion goes on the stresses build up in the
rocks until the stresses are large enough to cause
slip between the two adjoining portions of rocks
on either side A rupture takes place and the
strained rock rebounds back due to internal stress
Thus the strain energy in the rock is relieved
partly or fully (Fig 38)
Fault The interface between the plates where the movement has taken place is called fault
Slip When the rocky material along the interface of the plates in the Earthrsquos Crust reaches its
strength it fractures and a sudden movement called slip takes place
The sudden slip at the fault causes the earthquake A violent shaking of the Earth during
which large elastic strain energy released spreads out in the form of seismic waves that travel
through the body and along the surface of the
Earth
After elastic rebound there is a readjustment and
reapportion of the remaining strains in the region
The stress grows on a section of fault until slip
occurs again this causes yet another even though
smaller earthquake which is termed as aftershock
The aftershock activity continues until the
stresses are below the threshold level everywhere
in the rock
After the earthquake is over the process of strain build-up at this modified interface between the
tectonic plates starts all over again This is known as the Elastic Rebound Theory (Fig 39)
36 भको प और दोष क परकार Types of Earthquakes and Faults
Inter-plate Earthquakes Most earthquakes occurring along the boundaries of the tectonic
plates are called Inter-plate Earthquakes (eg 1897
Assam (India) earthquake)
Intra-plate Earthquakes Numbers of earthquakes
occurring within the plate itself but away from the
plate boundaries are called Intra-plate Earthquakes
(eg 1993 Latur (India) earthquake)
Note In both types of earthquakes the slip
generated at the fault during earthquakes is along
Fig 310 Type of Faults
Fig 38 Elastic Strain Build-Up and Brittle Rupture
Fig 39 Elastic Rebound Theory
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both vertical and horizontal directions (called Dip Slip) and lateral directions (called Strike
Slip) with one of them dominating sometimes (Fig 310)
37 जमीन कस तिलिी ि How the Ground shakes
Seismic waves Large strain energy released during an earthquake travels as seismic waves in all
directions through the Earthrsquos layers reflecting and refracting at each interface (Fig 311)
There are of two types of waves 1) Body Waves
2) Surface Waves
Body waves are of two types
a) Primary Waves (P-Wave)
b) Secondary Wave (S-Wave)
Surface waves are of two types namely
a) Love Waves
b) Rayleigh Waves
Body Waves Body waves have spherical wave front They consist of
Primary Waves (P-waves) Under P-waves [Fig 311(a)] material particles undergo
extensional and compressional strains along direction of energy transmission These waves
are faster than all other types of waves
Secondary Waves (S-waves) Under S-waves [Fig 311(b)] material particles oscillate at
Fig 311 Arrival of Seismic Waves at a Site
Fig 311(a) Motions caused by Primary Waves
Fig 311(b) Motions caused by Secondary Waves
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right angles to direction of energy transmission This type of wave shears the rock particle to
the direction of wave travel Since the liquid has no shearing resistance these waves cannot
pass through liquids
Surface Waves Surface waves have cylindrical wave front They consist of
Love Waves In case of Love waves [Fig 311(c)] the displacement is transverse with no
vertical or longitudinal components (ie similar to secondary waves with no vertical
component) Particle motion is restricted to near the surface Love waves being transverse
waves these cannot travel in liquids
Rayleigh Waves Rayleigh waves [Fig 311(d)] make a material particle oscillate in an
elliptic path in the vertical plane with horizontal motion along direction of energy
transmission
Note Primary waves are fastest followed in sequence by Secondary Love and Rayleigh waves
38 भको प या भको पी खिरो ो का परभाव Effects of Earthquake or Seismic Hazards
Basic causes of earthquake-induced damage are
Ground shaking
Structural hazards
Liquefaction
Ground failure Landslides
Tsunamis and
Fire
Fig 311(c) Motions caused by Love Waves
Fig 311(d) Motions caused by Rayleigh Waves
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381 जमीन को पन Ground shaking
Ground shaking can be considered to be the most important of all seismic hazards because all
the other hazards are caused by ground shaking
When an earthquake occurs seismic waves radiate away from the source and travel rapidly
through the earthrsquos crust
When these waves reach the ground surface they produce shaking that may last from seconds
to minutes
The strength and duration of shaking at a particular site depends on the size and location of
the earthquake and on the characteristics of the site
At sites near the source of a large earthquake ground shaking can cause tremendous damage
Where ground shaking levels are low the other seismic hazards may be low or nonexistent
Strong ground shaking can produce extensive damage from a variety of seismic hazards
depending upon the characteristics of the soil
The characteristics of the soil can greatly influence the nature of shaking at the ground
surface
Soil deposits tend to act as ldquofiltersrdquo to seismic waves by attenuating motion at certain
frequencies and amplifying it at others
Since soil conditions often vary dramatically over short distances levels of ground shaking
can vary significantly within a small area
One of the most important aspects of geotechnical earthquake engineering practice involves
evaluation of the effects of local soil conditions on strong ground motion
382 सोरचनातमक खिर Structural Hazards
Without doubt the most dramatic and memorable images of earthquake damage are those of
structural collapse which is the leading cause of death and economic loss in many
earthquakes
As the earth vibrates all buildings on the ground surface will respond to that vibration in
varying degrees
Earthquake induced accelerations velocities and displacements can damage or destroy a
building unless it has been designed and constructed or strengthened to be earthquake
resistant
The effect of ground shaking on buildings is a principal area of consideration in the design of
earthquake resistant buildings
Seismic design loads are extremely difficult to determine due to the random nature of
earthquake motions
Structures need not collapse to cause death and damage Falling objects such as brick facings
and parapets on the outside of a structure or heavy pictures and shelves within a structure
have caused casualties in many earthquakes Interior facilities such as piping lighting and
storage systems can also be damaged during earthquakes
However experiences from past strong earthquakes have shown that reasonable and prudent
practices can keep a building safe during an earthquake
Over the years considerable advancement in earthquake-resistant design has moved from an
emphasis on structural strength to emphases on both strength and ductility In current design
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practice the geotechnical earthquake engineer is often consulted for providing the structural
engineer with appropriate design ground motions
383 दरवीकरण Liquefaction
In some cases earthquake damage have occurred when soil deposits have lost their strength and
appeared to flow as fluids This phenomenon is termed as liquefaction In liquefaction the
strength of the soil is reduced often drastically to the point where it is unable to support
structures or remain stable Because it only occurs in saturated soils liquefaction is most
commonly observed near rives bays and other bodies of water
Soil liquefaction can occur in low density saturated sands of relatively uniform size The
phenomenon of liquefaction is particularly important for dams bridges underground pipelines
and buildings standing on such ground
384 जमीन तवफलिा लि सलाइि Ground Failure Land slides
1) Earthquake-induced ground Failure has been observed in the form of ground rupture along
the fault zone landslides settlement and soil liquefaction
2) Ground rupture along a fault zone may be very limited or may extend over hundreds of
kilometers
3) Ground displacement along the fault may be horizontal vertical or both and can be
measured in centimetres or even metres
4) A building directly astride such a rupture will be severely damaged or collapsed
5) Strong earthquakes often cause landslides
6) In a number of unfortunate cases earthquake-induced landslides have buried entire towns
and villages
7) Earthquake-induced landslides cause damage by destroying buildings or disrupting bridges
and other constructed facilities
8) Many earthquake-induced landslides result from liquefaction phenomenon
9) Others landslides simply represent the failures of slopes that were marginally stable under
static conditions
10) Landslide can destroy a building the settlement may only damage the building
385 सनामी Tsunamis
1) Tsunamis or seismic sea waves are generally produced by a sudden movement of the ocean
floor
2) Rapid vertical seafloor movements caused by fault rupture during earthquakes can produce
long-period sea waves ie Tsunamis
3) In the open sea tsunamis travel great distances at high speeds but are difficult to detect ndash
they usually have heights of less than 1 m and wavelengths (the distance between crests) of
several hundred kilometres
4) As a tsunami approaches shore the decreasing water depth causes its speed to decrease and
the height of the wave to increase
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5) As the water waves approach land their velocity decreases and their height increases from
5 to 8 m or even more
6) In some coastal areas the shape of the seafloor may amplify the wave producing a nearly
vertical wall of water that rushes far inland and causes devastating damage
7) Tsunamis can be devastating for buildings built in coastal areas
386 अति Fire
When the fire following an earthquake starts it becomes difficult to extinguish it since a strong
earthquake is accompanied by the loss of water supply and traffic jams Therefore the
earthquake damage increases with the earthquake-induced fire in addition to the damage to
buildings directly due to earthquakes
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अधयाय Chapter ndash 4
भको पी जोन और भको प का मापन Seismic Zone and Measurement of Earthquake
41 भको पी जोन Seismic Zone
Due to convective flow of mantle material crust of Earth and some portion of mantle slide on hot
molten outer core This sliding of Earthrsquos mass takes place in pieces called Tectonic Plates The
surface of the Earth consists of seven major tectonic plates (Fig 41)
They are
1 Eurasian Plate
2 Indo-Australian Plate
3 Pacific Plate
4 North American Plate
5 South American Plate
6 African Plate
7 Antarctic Plate
India lies at the northwestern end of the Indo Australian Plate (Fig 42) This Plate is colliding
against the huge Eurasian Plate and going under the Eurasian Plate Three chief tectonic sub-
regions of India are
the mighty Himalayas along the north
the plains of the Ganges and other rivers and
the peninsula
Most earthquakes occur along the Himalayan plate boundary (these are inter-plate earthquakes)
but a number of earthquakes have also occurred in the peninsular region (these are intra-plate
earthquakes)
Fig 41 Major Tectonic Plates on the Earthrsquos surface
Fig 42 Geographical Layout and Tectonic Plate
Boundaries in India
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Bureau of Indian Standards [IS1893 (part ndash 1) 2002] based on various scientific inputs from a
number of agencies including earthquake data supplied by Indian Meteorological Department
(IMD) has grouped the country into four seismic zones viz Zone II III IV and V Of these
Zone V is rated as the most seismically prone region while Zone II is the least (Fig 43)
Indian Seismic code (IS 18932002) divides the country into four seismic zones based on the
expected intensity of shaking in future earthquake The four zones correspond to areas that have
potential for shaking intensity on MSK scale as shown in the table
Seismic Zone Intensity on MSK scale of total area
II (Low intensity zone) VI (or less) 43
III (Moderate intensity zone) VII 27
IV (Severe intensity zone) VIII 18
V (Very Severe intensity zone) IX (and above) 12
Fig 43 Map showing Seismic Zones of India [IS 1893 (Part 1) 2002]
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42 भको प का मापन Measurement of Earthquake
421 मापन उपकरण Measuring Instruments
Seismograph The instrument that measures earthquake shaking is known as a seismograph
(Fig 44) It has three components ndash
Sensor ndash It consists of pendulum mass
string magnet and support
Recorder ndash It consists of drum pen and
chart paper
Timer ndash It consists of the motor that rotates
the drum at constant speed
Seismoscopes Some instruments that do not
have a timer device provide only the maximum
extent (or scope) of motion during the
earthquake
Digital instruments The digital instruments using modern computer technology records the
ground motion on the memory of the microprocessor that is in-built in the instrument
Note The analogue instruments have evolved over time but today digital instruments are more
commonly used
422 मापन क सकल Scale of Measurement
The Richter Magnitude Scale (also called Richter scale) assigns a magnitude number to quantify
the energy released by an earthquake Richter scale is a base 10 logarithmic scale which defines
magnitude as the logarithm of the ratio of the amplitude of the seismic wave to an arbitrary minor
amplitude
The magnitude M of an Earthquake is defined as
M = log10 A - log10 A0
Where
A = Recorded trace amplitude for that earthquake at a given distance as written by a
standard type of instrument (say Wood Anderson instrument)
A0 = Same as A but for a particular earthquake selected as standard
This number M is thus independent of distance between the epicentre and the station and is a
characteristic of the earthquake The standard shock has been defined such that it is low enough
to make the magnitude of most of the recorded earthquakes positive and is assigned a magnitude
of zero Thus if A = A0
Fig 44 Schematic of Early Seismograph
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M = log10 A0 - log10 A0 = 0
Standard shock of magnitude zero It is defined as one that records peak amplitude of one
thousandths of a millimetre at a distance of 100 km from the epicentre
1) Zero magnitude does not mean that there is no earthquake
2) Magnitude of an earthquake can be a negative number also
3) An earthquake that records peak amplitude of 1 mm on a standard seismograph at 100 km
will have its magnitude as
M = log10 (1) - log10 (10-3
)= 0 ndash (-3) = 3
Magnitude of a local earthquake It is defined as the logarithm to base 10 of the maximum
seismic wave amplitude (in thousandths of a mm) recorded on Wood Anderson seismograph at a
distance of 100 kms from the earthquake epicentre
1) With increase in magnitude by 10 the energy released by an earthquake increases by a
factor of about 316
2) A magnitude 80 earthquake releases about 316 times the energy released by a magnitude
70 earthquake or about 1000 times the energy released by a 60 earthquake
3) With increase in magnitude by 02 the energy released by the earthquake doubles
43 भको प पररमाण सकल क परकार Types of Earthquake Magnitude Scales
Several scales have historically been described as the ldquoRitcher Scalerdquo The Ritcher local
magnitude (ML) is the best known magnitude scale but it is not always the most appropriate scale
for description of earthquake size The Ritcher local magnitude does not distinguish between
different types of waves
At large epicentral distances body waves have usually been attenuated and scattered sufficiently
that the resulting motion is dominated by surface waves
Other magnitude scales that base the magnitude on the amplitude of a particular wave have been
developed They are
a) Surface Wave Magnitude (MS)
b) Body Wave Magnitude (Mb)
c) Moment Magnitude (Mw)
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431 सिि लिर पररमाण Surface Wave Magnitude (MS)
The surface wave magnitude (Gutenberg and Ritcher 1936) is a worldwide magnitude scale
based on the amplitude of Rayleigh waves with period of about 20 sec The surface wave
magnitude is obtained from
MS = log A + 166 log Δ + 20
Where A is the maximum ground displacement in micrometers and Δ is the epicentral distance of
the seismometer measured in degrees (3600 corresponding to the circumference of the earth)
The surface wave magnitude is most commonly used to describe the size of shallow (less than
about 70 km focal depth) distant (farther than about 1000 km) moderate to large earthquakes
432 बॉिी लिर पररमाण Body Wave Magnitude (Mb)
For deep-focus earthquakes surface waves are often too small to permit reliable evaluation of the
surface wave magnitude The body wave magnitude (Gutenberg 1945) is a worldwide magnitude
scale based on the amplitude of the first few cycles of p-waves which are not strongly influenced
by the focal depth (Bolt 1989) The body wave magnitude can be expressed as
Mb = log A ndash log T + 001Δ + 59
Where A is the p-wave amplitude in micrometers and T is the period of the p-wave (usually
about one sec)
Saturation
For strong earthquakes the measured
ground-shaking characteristics become
less sensitive to the size of the
earthquake than the smaller earthquakes
This phenomenon is referred to as
saturation (Fig 45)
The body wave and the Ritcher local
magnitudes saturate at magnitudes of 6
to 7 and the surface wave magnitude
saturates at about Ms = 8
To describe the size of a very large
earthquake a magnitude scale that does
not depend on ground-shaking levels
and consequently does not saturate
would be desirable
Fig 45 Saturation of various magnitude scale Mw (Moment
Magnitude) ML (Ritcher Local Magnitude) MS (Surface Wave
Magnitude) mb (Short-period Body Wave Magnitude) mB
(Long-period Body Wave Magnitude) and MJMA (Japanese
Meteorological Agency Magnitude)
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433 पल पररमाण Moment Magnitude (Mw)
The only magnitude scale that is not subject to saturation is the moment magnitude
The moment magnitude is given by
Mw = [(log M0)15] ndash 107
Where M0 is the seismic moment in dyne-cm
44 भको प िीवरिा Earthquake Intensity
Earthquake magnitude is simply a measure of the size of the earthquake reflecting the elastic
energy released by the earthquake It is usually referred by a certain real number on the Ritcher
scale (eg magnitude 65 earthquake)
On the other hand earthquake intensity indicates the extent of shaking experienced at a given
location due to a particular earthquake It is usually referred by a Roman numeral on the
Modified Mercalli Intensity (MMI) scale as given below
I Not felt except by a very few under especially favourable circumstances
II Felt by only a few persons at rest especially on upper floors of buildings delicately
suspended objects may swing
III Felt quite noticeably indoors especially on upper floors of buildings but many people
do not recognize it as an earthquake standing motor cars may rock slightly vibration
like passing of truck duration estimated
IV During the day felt indoors by many outdoors by few at night some awakened
dishes windows doors disturbed walls make cracking sound sensation like heavy
truck striking building standing motor cars rocked noticeably
V Felt by nearly everyone many awakened some dishes windows etc broken a few
instances of cracked plaster unstable objects overturned disturbances of trees piles
and other tall objects sometimes noticed pendulum clocks may stop
VI Felt by all many frightened and run outdoors some heavy furniture moved a few
instances of fallen plaster or damaged chimneys damage slight
VII Everybody runs outdoors damage negligible in buildings of good design and
construction slight to moderate in well-built ordinary structures considerable in
poorly built or badly designed structures some chimneys broken noticed by persons
driving motor cars
VIII Damage slight in specially designed structures considerable in ordinary substantial
buildings with partial collapse great in poorly built structures panel walls thrown out
of frame structures fall of chimneys factory stacks columns monuments walls
heavy furniture overturned sand and mud ejected in small amounts changes in well
water persons driving motor cars disturbed
IX Damage considerable in specially designed structures well-designed frame structures
thrown out of plumb great in substantial buildings with partial collapse buildings
shifted off foundations ground cracked conspicuously underground pipes broken
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X Some well-built wooden structures destroyed most masonry and frame structures
destroyed with foundations ground badly cracked rails bent landslides considerable
from river banks and steep slopes shifted sand and mud water splashed over banks
XI Few if any (masonry) structures remain standing bridges destroyed broad fissures in
ground underground pipelines completely out of service earth slumps and land slips
in soft ground rails bent greatly
XII Damage total practically all works of construction are damaged greatly or destroyed
waves seen on ground surface lines of sight and level are destroyed objects thrown
into air
441 MSK िीवरिा सकल MSK Intensity Scale
The MSK intensity scale is quite comparable to the Modified Mercalli intensity scale but is more
convenient for application in field and is widely used in India In assigning the MSK intensity
scale at a site due attention is paid to
Type of Structures (Table ndash A)
Percentage of damage to each type of structure (Table ndash B)
Grade of damage to different types of structures (Table ndash C)
Details of Intensity Scale (Table ndash D)
The main features of MSK intensity scale are as follows
Table ndash A Types of Structures (Buildings)
Type of
Structures
Definitions
A Building in field-stone rural structures unburnt ndash brick houses clay houses
B Ordinary brick buildings buildings of large block and prefabricated type half
timbered structures buildings in natural hewn stone
C Reinforced buildings well built wooden structures
Table ndash B Definition of Quantity
Quantity Percentage
Single few About 5 percent
Many About 50 percent
Most About 75 percent
Table ndash C Classification of Damage to Buildings
Grade Definitions Descriptions
G1 Slight damage Fine cracks in plaster fall of small pieces of plaster
G2 Moderate damage Small cracks in plaster fall of fairly large pieces of plaster
pantiles slip off cracks in chimneys parts of chimney fall down
G3 Heavy damage Large and deep cracks in plaster fall of chimneys
G4 Destruction Gaps in walls parts of buildings may collapse separate parts of
the buildings lose their cohesion and inner walls collapse
G5 Total damage Total collapse of the buildings
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Table ndash D Details of Intensity Scale
Intensity Descriptions
I Not noticeable The intensity of the vibration is below the limits of sensibility
the tremor is detected and recorded by seismograph only
II Scarcely noticeable
(very slight)
Vibration is felt only by individual people at rest in houses
especially on upper floors of buildings
III Weak partially
observed only
The earthquake is felt indoors by a few people outdoors only in
favourable circumstances The vibration is like that due to the
passing of a light truck Attentive observers notice a slight
swinging of hanging objects somewhat more heavily on upper
floors
IV Largely observed The earthquake is felt indoors by many people outdoors by few
Here and there people awake but no one is frightened The
vibration is like that due to the passing of a heavily loaded truck
Windows doors and dishes rattle Floors and walls crack
Furniture begins to shake Hanging objects swing slightly Liquid
in open vessels are slightly disturbed In standing motor cars the
shock is noticeable
V Awakening
a) The earthquake is felt indoors by all outdoors by many Many
people awake A few run outdoors Animals become uneasy
Buildings tremble throughout Hanging objects swing
considerably Pictures knock against walls or swing out of
place Occasionally pendulum clocks stop Unstable objects
overturn or shift Open doors and windows are thrust open
and slam back again Liquids spill in small amounts from
well-filled open containers The sensation of vibration is like
that due to heavy objects falling inside the buildings
b) Slight damages in buildings of Type A are possible
c) Sometimes changes in flow of springs
VI Frightening
a) Felt by most indoors and outdoors Many people in buildings
are frightened and run outdoors A few persons loose their
balance Domestic animals run out of their stalls In few
instances dishes and glassware may break and books fall
down Heavy furniture may possibly move and small steeple
bells may ring
b) Damage of Grade 1 is sustained in single buildings of Type B
and in many of Type A Damage in few buildings of Type A
is of Grade 2
c) In few cases cracks up to widths of 1cm possible in wet
ground in mountains occasional landslips change in flow of
springs and in level of well water are observed
VII Damage of buildings
a) Most people are frightened and run outdoors Many find it
difficult to stand The vibration is noticed by persons driving
motor cars Large bells ring
b) In many buildings of Type C damage of Grade 1 is caused in
many buildings of Type B damage is of Grade 2 Most
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buildings of Type A suffer damage of Grade 3 few of Grade
4 In single instances landslides of roadway on steep slopes
crack inroads seams of pipelines damaged cracks in stone
walls
c) Waves are formed on water and is made turbid by mud stirred
up Water levels in wells change and the flow of springs
changes Sometimes dry springs have their flow resorted and
existing springs stop flowing In isolated instances parts of
sand and gravelly banks slip off
VIII Destruction of
buildings
a) Fright and panic also persons driving motor cars are
disturbed Here and there branches of trees break off Even
heavy furniture moves and partly overturns Hanging lamps
are damaged in part
b) Most buildings of Type C suffer damage of Grade 2 and few
of Grade 3 Most buildings of Type B suffer damage of Grade
3 Most buildings of Type A suffer damage of Grade 4
Occasional breaking of pipe seams Memorials and
monuments move and twist Tombstones overturn Stone
walls collapse
c) Small landslips in hollows and on banked roads on steep
slopes cracks in ground up to widths of several centimetres
Water in lakes becomes turbid New reservoirs come into
existence Dry wells refill and existing wells become dry In
many cases change in flow and level of water is observed
IX General damage of
buildings
a) General panic considerable damage to furniture Animals run
to and fro in confusion and cry
b) Many buildings of Type C suffer damage of Grade 3 and a
few of Grade 4 Many buildings of Type B show a damage of
Grade 4 and a few of Grade 5 Many buildings of Type A
suffer damage of Grade 5 Monuments and columns fall
Considerable damage to reservoirs underground pipes partly
broken In individual cases railway lines are bent and
roadway damaged
c) On flat land overflow of water sand and mud is often
observed Ground cracks to widths of up to 10 cm on slopes
and river banks more than 10 cm Furthermore a large
number of slight cracks in ground falls of rock many
landslides and earth flows large waves in water Dry wells
renew their flow and existing wells dry up
X General destruction of
building
a) Many buildings of Type C suffer damage of Grade 4 and a
few of Grade 5 Many buildings of Type B show damage of
Grade 5 Most of Type A have destruction of Grade 5
Critical damage to dykes and dams Severe damage to
bridges Railway lines are bent slightly Underground pipes
are bent or broken Road paving and asphalt show waves
b) In ground cracks up to widths of several centimetres
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sometimes up to 1m Parallel to water courses occur broad
fissures Loose ground slides from steep slopes From river
banks and steep coasts considerable landslides are possible
In coastal areas displacement of sand and mud change of
water level in wells water from canals lakes rivers etc
thrown on land New lakes occur
XI Destruction
a) Severe damage even to well built buildings bridges water
dams and railway lines Highways become useless
Underground pipes destroyed
b) Ground considerably distorted by broad cracks and fissures
as well as movement in horizontal and vertical directions
Numerous landslips and falls of rocks The intensity of the
earthquake requires to be investigated specifically
XII Landscape changes
a) Practically all structures above and below ground are greatly
damaged or destroyed
b) The surface of the ground is radically changed Considerable
ground cracks with extensive vertical and horizontal
movements are observed Falling of rock and slumping of
river banks over wide areas lakes are dammed waterfalls
appear and rivers are deflected The intensity of the
earthquake requires to be investigated specially
442 तवतभनन सकलो ो की िीवरिा मलो ो की िलना Comparison of Intensity Values of
Different Scales
443 तवतभनन पररमाण और िीवरिा क भको प का परभाव Effect of Earthquake of various
Magnitude and Intensity
The following describes the typical effects of earthquakes of various magnitudes near the
epicenter The values are typical only They should be taken with extreme caution since intensity
and thus ground effects depend not only on the magnitude but also on the distance to the
epicenter the depth of the earthquakes focus beneath the epicenter the location of the epicenter
and geological conditions (certain terrains can amplify seismic signals)
Fig 45 Comparison of Intensity Values of Different Scales
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Magnitude Description Mercalli
intensity
Average earthquake effects Average
frequency of
occurrence
(estimated)
10-19 Micro I Micro earthquakes not felt or felt rarely
Recorded by seismographs
Continualseveral
million per year
20-29 Minor I to II Felt slightly by some people No damage to
buildings
Over one million
per year
30-39 III to IV Often felt by people but very rarely causes
damage Shaking of indoor objects can be
noticeable
Over 100000 per
year
40-49 Light IV to VI Noticeable shaking of indoor objects and
rattling noises Felt by most people in the
affected area Slightly felt outside
Generally causes none to minimal damage
Moderate to significant damage very
unlikely Some objects may fall off shelves
or be knocked over
10000 to 15000
per year
50-59 Moderate VI to
VIII
Can cause damage of varying severity to
poorly constructed buildings At most none
to slight damage to all other buildings Felt
by everyone
1000 to 1500 per
year
60-69 Strong VII to X Damage to a moderate number of well-built
structures in populated areas Earthquake-
resistant structures survive with slight to
moderate damage Poorly designed
structures receive moderate to severe
damage Felt in wider areas up to hundreds
of mileskilometers from the epicenter
Strong to violent shaking in epicentral area
100 to 150 per
year
70-79 Major VIII or
Greater
Causes damage to most buildings some to
partially or completely collapse or receive
severe damage Well-designed structures
are likely to receive damage Felt across
great distances with major damage mostly
limited to 250 km from epicenter
10 to 20 per year
80-89 Great Major damage to buildings structures
likely to be destroyed Will cause moderate
to heavy damage to sturdy or earthquake-
resistant buildings Damaging in large
areas Felt in extremely large regions
One per year
90 and
greater
At or near total destruction ndash severe damage
or collapse to all buildings Heavy damage
and shaking extends to distant locations
Permanent changes in ground topography
One per 10 to 50
years
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45 भको प तनगरानी और सवाओो क तलए एजतसयो ो Agencies for Earthquake Monitoring and
Services
Centre for Seismology (CS) in Indian Meteorological Department (IMD) under Ministry of
Earth Sciences is nodal agency of Government of India dealing with various activities in
the field of seismology and allied disciplines and is responsible for monitoring seismic
activity in and around the country
The major activities currently being pursued by the Centre for Seismology (CS) include
a) Earthquake monitoring on 24X7 basis including real time seismic monitoring for early
warning of tsunamis
b) Operation and maintenance of national seismological network and local networks
c) Seismological data centre and information services
d) Seismic hazard and risk related studies
e) Field studies for aftershock swarm monitoring site response studies
f) Earthquake processes and modelling etc
These activities are being managed by various unitsgroups of the Centre for Seismology
(CS) as detailed below
1) Centre for Seismology (CS) is maintaining a country wide National Seismological
Network (NSN) consisting of a total of 82 seismological stations spread over the
entire length and breadth of the country This includes
a) 16-station V-SAT based digital seismic telemetry system around National Capital
Territory (NCT) of Delhi
b) 20-station VSAT based real time seismic monitoring network in North East region
of the country
(c) 17-station Real Time Seismic Monitoring Network (RTSMN) to monitor and
report large magnitude under-sea earthquakes capable of generating tsunamis on
the Indian coastal regions
2) The remaining stations are of standalone analog type
3) A Control Room is in operation on a 24X7 basis at premises of IMD Headquarters in
New Delhi with state-of-the art facilities for data collection processing and
dissemination of information to the concerned user agencies
4) India represented by CSIMD is a permanent Member of the International
Seismological Centre (ISC) UK
5) Seismological Bulletins of CSIMD are shared regularly with International
Seismological Centre (ISC) UK for incorporation in the ISCs Monthly Seismological
Bulletins which contain information on earthquakes occurring all across the globe
6) Towards early warning of tsunamis real-time continuous seismic waveform data of
three IMD stations viz Portblair Minicoy and Shillong is shared with global
community through IRIS (Incorporated Research Institutions of Seismology)
Washington DC USA
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अधयाय Chapter ndash 5
भवन म भको प परतिरोध म सधार क तलए सामानय तसदाोि General Principle for improving Earthquake Resistance in Building
51 िलकापन Lightness
Since the earthquake force is a function of mass the building should be as light as possible
consistent with structural safety and functional requirements Roofs and upper storeys of
buildings in particular should be designed as light as possible
52 तनमायण की तनरोिरिा Continuity of Construction
As far as possible all parts of the building should be tied together in such a manner that
the building acts as one unit
For integral action of building roof and floor slabs should be continuous throughout as
far as possible
Additions and alterations to the structures should be accompanied by the provision of
positive measures to establish continuity between the existing and the new construction
53 परोजककटोग एवो ससिि पाटटयस Projecting and Suspended Parts
Projecting parts should be avoided as far as possible If the projecting parts cannot be
avoided they should be properly reinforced and firmly tied to the main structure
Ceiling plaster should preferably be avoided When it is unavoidable the plaster should
be as thin as possible
Suspended ceiling should be avoided as far as possible Where provided they should be
light and adequately framed and secured
54 भवन की आकति Shape of Building
In order to minimize torsion and stress concentration the building should have a simple
rectangular plan
It should be symmetrical both with respect to mass and rigidity so that the centre of mass
and rigidity of the building coincide with each other
It will be desirable to use separate blocks of rectangular shape particularly in seismic
zones V and IV
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55 सतवधा जनक तबकडोग लआउट Preferred Building Layouts
Buildings having plans with shapes like L T E and Y shall preferably be separated into
rectangular parts by providing separation sections at appropriate places Typical examples are
shown in Fig 51
56 तवतभनन तदशाओो म शककत Strength in Various Directions
The structure shall have adequate strength against earthquake effects along both the horizontal
axes considering the reversible nature of earthquake forces
57 नी ोव Foundations
For the design of foundations the provisions of IS 1904 1986 in conjunctions with IS
1893 1984 shall generally be followed
The sub-grade below the entire area of the building shall preferably be of the same type of
the soil Wherever this is not possible a suitably located separation or crumple section shall
be provided
Loose fine sand soft silt and expansive clays should be avoided If unavoidable the
building shall rest either on a rigid raft foundation or on piles taken to a firm stratum
However for light constructions the following measures may be taken to improve the soil
on which the foundation of the building may rest
a) Sand piling and b) Soil stabilization
Structure shall not be founded on loose soil which will subside or liquefy during an
earthquake resulting in large differential settlement
58 छि एवो मोतजल Roofs and Floors
581 सपाट छि या फशय Flat roof or floor
Flat roof or floor shall not preferably be made of terrace of ordinary bricks supported on steel
timber or reinforced concrete joists nor they shall be of a type which in the event of an
earthquake is likely to be loosened and parts of all of which may fall If this type of construction
cannot be avoided the joists should be blocked at ends and bridged at intervals such that their
spacing is not altered during an earthquake
Fig 51 Typical Shapes of Building with Separation Sections [IS 4326 1993]
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582 ढलान वाली छि Pitched Roofs
For pitched roofs corrugated iron or asbestos sheets should be used in preference to
country Allahabad or Mangalore tiles or other loose roofing units
All roofing materials shall be properly tied to the supporting members
Heavy roofing materials should generally be avoided
583 सोवि छि Pent Roofs
All roof trusses should be supported on and fixed to timber band reinforced concrete band or
reinforced brick band The holding down bolts should have adequate length as required for
earthquake and wind forces
Where a trussed roof adjoins a masonry gable the ends of the purlins should be carried on and
secured to a plate or bearer which should be adequately bolted to timber reinforced concrete or
reinforced brick band at the top of gable end masonry
- At tie level all the trusses and the gable end should be provided with diagonal braces in plan
so as to transmit the lateral shear due to earthquake force to the gable walls acting as shear
walls at the ends
NOTE ndash Hipped roof in general have shown better structural behaviour during earthquakes than gable
ended roofs
584 जक मिराब Jack Arches
Jack arched roofs or floors where used should be provided with mild steel ties in all spans along
with diagonal braces in plan to ensure diaphragm actions
59 सीतढ़याो Staircases
The interconnection of the stairs with the adjacent floors should be appropriately treated by
providing sliding joints at the stairs to eliminate their bracing effect on the floors
Ladders may be made fixed at one end and freely resting at the other
Large stair halls shall preferably be separated from rest of the building by means of
separation or crumple section
Three types of stair construction may be adopted as described below
591 अलग सीतढ़याो Separated Staircases
One end of the staircase rests on a wall and the other end is carried by columns and beams which
have no connection with the floors The opening at the vertical joints between the floor and the
staircase may be covered either with a tread plate attached to one side of the joint and sliding on
the other side or covered with some appropriate material which could crumple or fracture during
an earthquake without causing structural damage
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The supporting members columns or walls are
isolated from the surrounding floors by means of
separation or crumple sections A typical
example is shown in Fig 52
592 तबलट-इन सीतढ़याो Built-in Staircase
When stairs are built monolithically with floors they can be protected against damage by
providing rigid walls at the stair opening An arrangement in which the staircase is enclosed by
two walls is given in Fig 53 (a) In such cases the joints as mentioned in respect of separated
staircases will not be necessary
The two walls mentioned above enclosing the staircase shall extend through the entire height of
the stairs and to the building foundations
Fig 53 (a) Rigidly Built-In Staircase [IS 4326 1993]
Fig 52 Separated Staircase
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593 सलाइतिोग जोड़ो ो वाली सीतढ़याो Staircases with Sliding Joints
In case it is not possible to provide rigid walls around stair openings for built-in staircase or to
adopt the separated staircases the staircases shall have sliding joints so that they will not act as
diagonal bracing (Fig 53 (b))
510 बॉकस परकार तनमायण Box Type Construction
This type of construction consists of prefabricated or in-situ masonry wall along with both the
axes of the building The walls support vertical loads and also act as shear walls for horizontal
loads acting in any direction All traditional masonry construction falls under this category In
prefabricated wall construction attention should be paid to the connections between wall panels
so that transfer of shear between them is ensured
511 अति सरकषा Fire Safety
Fire frequently follows an earthquake and therefore buildings should be constructed to make
them fire resistant in accordance with the provisions of relevant Indian Standards for fire safety
The relevant Indian Standards are IS 1641 1988 IS 1642 1989 IS 1643 1988 IS 1644 1988
and IS 1646 1986
Fig 53 (b) Staircase with Sliding Joint
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अधयाय Chapter ndash 6
भको प क दौरान आर सी भवनो ो क परदशयन पर सटरकचरल अतनयतमििाओो का परभाव Effect of Structural Irregularities on Performance of RC Buildings during Earthquakes
61 सटरकचरल अतनयतमििाओो का परभाव Effect of Structural Irregularities
There are numerous examples of past earthquakes in which the cause of failure of reinforced
concrete building has been ascribed to irregularities in configurations
Irregularities are mainly categorized as
(i) Horizontal Irregularities
(ii) Vertical Irregularities
62 कषतिज अतनयतमििाएो Horizontal Irregularities
Horizontal irregularities refer to asymmetrical plan shapes (eg L- T- U- F-) or discontinuities
in the horizontal resisting elements (diaphragms) such as cut-outs large openings re-entrant
corners and other abrupt changes resulting in torsion diaphragm deformations stress
concentration
Table ndash 61 Definitions of Irregular Buildings ndash Plan Irregularities (Fig 61)
S
No
Irregularity Type and Description
(i) Torsion Irregularity To be considered when floor diaphragms are rigid in their own
plan in relation to the vertical structural elements that resist the lateral forces Torsional
irregularity to be considered to exist when the maximum storey drift computed with
design eccentricity at one end of the structures transverse to an axis is more than 12
times the average of the storey drifts at the two ends of the structure
Fig 61 (a)
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(ii) Re-entrant Corners Plan configurations of a structure and its lateral force resisting
system contain re-entrant corners where both projections of the structure beyond the re-
entrant corner are greater than 15 percent of its plan dimension in the given direction
Fig 61 (b)
(iii) Diaphragm Discontinuity Diaphragms with abrupt discontinuities or variations in
stiffness including those having cut-out or open areas greater than 50 percent of the
gross enclosed diaphragm area or changes in effective diaphragm stiffness of more than
50 percent from one storey to the next
Fig 61 (c)
(iv) Out-of-Plane Offsets Discontinuities in a lateral force resistance path such as out-of-
plane offsets of vertical elements
Fig 61 (d)
(v) Non-parallel Systems The vertical elements
resisting the lateral force are not parallel to or
symmetric about the major orthogonal axes or the
lateral force resisting elements
Fig 61 (e)
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63 ऊरधायधर अतनयतमििाएो Vertical Irregularities
Vertical irregularities referring to sudden change of strength stiffness geometry and mass result
in irregular distribution of forces and or deformation over the height of building
Table ndash 62 Definition of Irregular Buildings ndash Vertical Irregularities (Fig 62)
S
No
Irregularity Type and Description
(i) a) Stiffness Irregularity ndash Soft Storey A soft storey is one in which the lateral stiffness is
less than 70 percent of that in the storey above or less than 80 percent of the average lateral
stiffness of the three storeys above
b) Stiffness Irregularity ndash Extreme Soft Storey A extreme soft storey is one in which the
lateral stiffness is less than 60 percent of that in the storey above or less than 70 percent of
the average stiffness of the three storeys above For example buildings on STILTS will fall
under this category
Fig 62 (a)
(ii) Mass Irregularity Mass irregularity shall be considered to exist where the seismic weight
of any storey is more than 200percent of that of its adjacent storeys The irregularity need
not be considered in case of roofs
Fig 62 (b)
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(iii) Vertical Geometric Irregularity Vertical geometric irregularity shall be considered to
exist where the horizontal dimension of the lateral force resisting system in any storey is
more than150 percent of that in its adjacent storey
Fig 62 (c)
(iv) In-Plane Discontinuity in Vertical Elements Resisting Lateral Force A in-plane offset of
the lateral force resisting elements greater than the length of those elements
Fig 62 (d)
(v) Discontinuity in Capacity ndash Weak Storey A weak storey is one in which the storey lateral
strength is less than 80 percent of that in the storey above The storey lateral strength is the
total strength of all seismic force resisting elements sharing the storey shear in the
considered direction
64 भवन तवनयास अतनयतमििाएो ndash सरसकयमए ववशलषण एव तनदमन क उपमय Building
Irregularities ndash Problems Analysis and Remedial Measures
The influence of irregularity on performance of building during earthquakes is presented to
account for the effects of these irregularities in analysis of problems and their solutions along
with the design
Vertical Geometric Irregularity when L2gt15 L1
In-Plane Discontinuity in Vertical Elements Resisting Weak Storey when Filt08Fi+ 1
Lateral Force when b gta
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Architectural problems Structural problems Remedial measures
Extreme heightdepth ratio
High overturning forces large drift causing non-structural damage foundation stability
Revive properties or special structural system
Extreme plan area Built-up large diaphragm forces Subdivide building by seismic joints
Extreme length depth ratio
Built-up of large lateral forces in perimeter large differences in resistance of two axes Experience greater variations in ground movement and soil conditions
Subdivide building by seismic joints
Variation in perimeter strength-stiffness
Torsion caused by extreme variation in strength and stiffness
Add frames and disconnect walls or use frames and lightweight walls
False symmetry Torsion caused by stiff asymmetric core Disconnect core or use frame with non-structural core walls
Re-entrant corners Torsion stress concentrations at the notches
Separate walls uniform box centre box architectural relief diagonal reinforcement
Mass eccentricities Torsion stress concentrations Reprogram or add resistance around mass to balance resistance and mass
Vertical setbacks and reverse setbacks
Stress concentration at notch different periods for different parts of building high diaphragm forces to transfer at setback
Special structural systems careful dynamic analysis
Soft storey frame Causes abrupt changes of stiffness at point of discontinuity
Add bracing add columns braced
Variation in column stiffness
Causes abrupt changes of stiffness much higher forces in stiffer columns
Redesign structural system to balance stiffness
Discontinuous shear wall Results in discontinuities in load path and stress concentration for most heavily loaded elements
Primary concern over the strength of lower level columns and connecting beams that support the load of discontinuous frame
Weak column ndash strong beam
Column failure occurs before beam short column must try and accommodate storey height displacement
Add full walls to reduce column forces or detach spandrels from columns or use light weight curtain wall with frame
Modification of primary structure
Most serious when masonry in-fill modifies structural concept creation of short stiff columns result in stress concentration
Detach in-fill or use light-weight materials
Building separation (Pounding)
Possibility of pounding dependent on building period height drift distance
Ensure adequate separation assuming opposite building vibrations
Coupled Incompatible deformation between walls and links
Design adequate link
Random Openings Seriously degrade capacity at point of maximum force transfer
Careful designing adequate space for reinforcing design
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अधयाय Chapter ndash 7
भवन की िायनातमक तवशषिाएा Dynamic Characteristics of Building
71 िायनातमक तवशषिाएा Dynamic Characteristics
Buildings oscillate during earthquake shaking The oscillation causes inertia force to be induced
in the building The intensity and duration of oscillation and the amount of inertia force induced
in a building depend on features of buildings called dynamic characteristics of building
The important dynamic characteristics of buildings are
a) Modes of Oscillation
b) Damping
A mode of oscillation of a building is defined by associated Natural Period and Deformed Shape
in which it oscillates Every building has a number of natural frequencies at which it offers
minimum resistance to shaking induced by external effects (like earthquakes and wind) and
internal effects(like motors fixed on it) Each of these natural frequencies and the associated
deformation shape of a building constitute a Natural Mode of Oscillation
The mode of oscillation with the smallest natural frequency (and largest natural period) is called
the Fundamental Mode the associated natural period T1is called the Fundamental Natural
Period
72 पराकतिक अवतध Natural Period
Natural Period (Tn) of a building is the time taken by it to undergo one complete cycle of
oscillation It is an inherent property of a building controlled by its mass m and stiffness k These
three quantities are related by
Its unit is second (s)
73 पराकतिक आवततत Natural Frequency
The reciprocal (1Tn) of natural period of a building is called the Natural Frequency fn its unit is
Hertz (Hz)
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74 पराकतिक अवतध को परभातवि करन वाल कारक Factors influencing Natural Period
741 कठोरिा का परभाव Effect of Stiffness Stiffer buildings have smaller natural period
742 दरवयमान का परभाव Effect of Mass Heavier buildings have larger natural period
743 कॉलम अतभतवनयास का परभाव Effect of Column Orientation Buildings with larger
column dimension oriented in the direction reduces the translational natural period of oscillation
in that direction
Fig 72 Effect of Mass
Fig 71 Effect of Stiffness
Fig 73 Effect of Column Orientation
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744 भवन की ऊो चाई का परभाव Effect of Building Height Taller buildings have larger
natural period
745 Unreinforced तचनाई भराव का परभाव Effect of Unreinforced Masonry Infills Natural
Period of building is lower when the stiffness contribution of URM infill is considered
Fig 75 Effect of Building Height
Fig 74 Effect of Building Height
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75 Mode आकति Mode Shape
Mode shape of oscillation associated with a natural period of a building is the deformed shape of
the building when shaken at the natural period Hence a building has as many mode shapes as
the number of natural periods
The deformed shape of the building associated with oscillation at fundamental natural period is
termed its first mode shape Similarly the deformed shapes associated with oscillations at
second third and other higher natural periods are called second mode shape third mode shape
and so on respectively
Fundamental Mode Shape of Oscillation
As shown in Fig 76 there are three basic modes of oscillation namely
1 Pure translational along X-direction
2 Pure translational along Y-direction and
3 Pure rotation about Z-axis
Regular buildings
These buildings have pure mode shapesThe Basic modes of oscillation ie two translational and
one rotational mode shapes
Irregular buildings
These buildings that have irregular geometry non-uniform distribution of mass and stiffness in
plan and along the height have mode shapes which are a mixture of these pure mode shapes
Each of these mode shapes is independent implying it cannot be obtained by combining any or
all of the other mode shapes
a) Fundamental and two higher translational modes of oscillation along X-direction of a
five storey benchmark building First modes shape has one zero crossing of the un-deformed
position second two and third three
Fig 76 Basic modes of oscillation
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b) Diagonal modes of oscillation First three modes of oscillation of a building symmetric in
both directions in plan first and second are diagonal translational modes and third rotational
c) Effect of modes of oscillation on column bending Columns are severely damaged while
bending about their diagonal direction
Fig 77 Fundamental and two higher translational modes of oscillation
along X-direction of a five storey benchmark building
Fig 78 Diagonal modes of oscillation
Fig 79 Effect of modes of oscillation on column bending
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76 Mode आकतियो ो को परभातवि करन वाल कारक Factors influencing Mode Shapes
761 Effect of relative flexural stiffness of structural elements Fundamental translational
mode shape changes from flexural-type to shear-type with increase in beam flexural stiffness
relative to that of column
762 Effect of axial stiffness of vertical members Fundamental translational mode shape
changes from flexure-type to shear-type with increase in axial stiffness of vertical members
Fig 710 Effect of relative flexural stiffness of structural elements
Fig 711 Effect of axial stiffness of vertical members
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763 Effect of degree of fixity at member ends Lack of fixity at beam ends induces flexural-
type behaviour while the same at column bases induces shear-type behaviour to the fundamental
translational mode of oscillation
Fig 712 Effect of degree of fixity at member ends
764 Effect of building height Fundamental translational mode shape of oscillation does not
change significantly with increase in building height unlike the fundamental translational natural
period which does change
Fig 713 Effect of building height
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765 Influence of URM Infill Walls in Mode Shape of RC frame Buildings Mode shape of
a building obtained considering stiffness contribution of URM is significantly different from that
obtained without considering the same
77 सोरचना की परतितकरया Response of Structure
The earthquakes cause vibratory motion which is cyclic about the equilibrium The structural
response is vibratory (Dynamic) and it is cyclic about the equilibrium position of structure The
fundamental natural frequency of most civil engineering structures lie in the range of 01 sec to
30 sec or so This is also the range of frequency content of earthquake-generated ground
motions Hence the ground motion imparts considerable amount of energy to the structures
Initially the structure responds elastically to the ground motion however as its yield capacity is
exceeded the structure responds in an inelastic manner During the inelastic response stiffness
and energy dissipation properties of the structure are modified
Response of the structure to a given strong ground motion depends not only on the properties of
input ground motion but also on the structural properties
78 तिजाइन सकटर म Design Spectrum
The design spectrum is a design specification which is arrived at by considering all aspects The
design spectrum may be in terms of acceleration velocity or displacement
Fig 714 Influence of URM Infill Walls in Mode Shape of RC frame Buildings
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Since design spectrum is a specification for design it cannot be viewed in isolation without
considering the other factors that go into the design process One must concurrently specify
a) The procedure to calculate natural period of the structure
b) The damping to be used for a given type of structure
c) The permissible stresses and strains load factors etc
Unless this information is part of a design spectrum the design specification is incomplete
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अधयाय Chapter ndash 8
डिजमइन पमशवा बलो क तनधमारण क ललए कोि आधमररि िरीकम Code based Procedure for Determination of Design Lateral Loads
81 भको पी तिजाइन की तफलोसफ़ी Philosophy of Seismic Design
Design of earthquake effect is not termed as Earthquake Proof Design Actual forces that appear
on structure during earthquake are much greater than the design forces Complete protection
against earthquake of all size is not economically feasible and design based alone on strength
criteria is not justified Earthquake demand is estimated only based on concept of probability of
exceedance Design of earthquake effect is therefore termed as Earthquake Resistant Design
against the probable value of demand
Maximum Considered Earthquake (MCE) The earthquake corresponding to the Ultimate
Safety Requirement is often called as Maximum Considered Earthquake
Design Basis Earthquake (DBE) It is defined as the Maximum Earthquake that reasonably can
be expected to experience at the site during lifetime of structure
The philosophy of seismic design is to ensure that structures possess at least a minimum strength
to
(i) resist minor (lt DBE) which may occur frequently without damage
(ii) resist moderate earthquake (DBE) without significant structural damage through some
non-structural damage
(iii) resist major earthquake (MCE) without collapse
82 भको पी तवशलषण क तलए िरीक Methods for Seismic Analysis
The response of a structure to ground vibrations is a function of the nature of foundation soil
materials form size and mode of construction of structures and duration and characteristics of
ground motion Code specifies design forces for structures standing on rock or firm soils which
do not liquefy or slide due to loss of strength during ground motion
Analysis is carried out by
a- Dynamic analysis procedure [Clause 78 of IS 1893 (Part I) 2002]
b- Simplified method referred as Lateral Force Procedure [Clause 75 of IS 1893 (Part I)
2002] also recognized as Equivalent Lateral Force Procedure or Equivalent Static
Procedure in the literature
The main difference between the equivalent lateral force procedure and dynamic analysis
procedure lies in the magnitude and distribution of lateral forces over the height of the buildings
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In the dynamic analysis procedure the lateral forces are based on the properties of the natural
vibration modes of the building which are determined by the distribution of mass and stiffness
over height In the equivalent lateral force procedures the magnitude of forces is based on an
estimation of the fundamental period and on the distribution of forces as given by simple
formulae appropriate for regular buildings
83 िायनातमक तवशलषण Dynamic Analysis
Dynamic analysis shall be performed to obtain the design seismic force and its distribution to
different levels along the height of the building and to the various lateral load resisting elements
for the following buildings
a) Regular buildings ndash Those greater than 40 m in height in Zones IV and V and those greater
than 90 m in height in Zones II and III Modelling as per Para 7845 of IS 1893 (Part 1)
2002 can be used
b) Irregular buildings (as defined in Table ndash 61 and Table ndash 62 of Chapter - 6) ndash All framed
buildings higher than 12m in Zones IV and V and those greater than 40m in height in Zones
II and III
84 पारशय बल परतकरया Lateral Force Procedure
The random earthquake ground motions which cause the structure to vibrate can be resolved in
any three mutually perpendicular directions The predominant direction of ground vibration is
usually horizontal
The codes represent the earthquake-induced inertia forces in the form of design equivalent static
lateral force This force is called as the Design Seismic Base Shear VB VB remains the primary
quantity involved in force-based earthquake-resistant design of buildings
The Design Seismic Base Shear VB is given by
Where Ah = Design horizontal seismic coefficient for a structure
=
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Z = Zone Factor
It is for the Maximum Considered Earthquake (MCE) and service life of structure in a zone
Generally Design Basis Earthquake (DBE) is half of Maximum Considered Earthquake
(MCE) The factor 2 in the denominator of Z is used so as to reduce the MCE zone factor to
the factor for DBE
The value of Ah will not be taken less than Z2 whatsoever the value of IR
The value of Zone Factor is given in Table ndash 81
Table ndash 81 Zone Factor Z[IS 1893 (Part 1) 2002]
Seismic Zone II III IV V
Seismic Intensity Low Moderate Severe Very Severe
Zone Factor Z 010 016 024 036
I = Importance Factor
Value of importance factor depends upon the functional use of the structures characterized
by hazardous consequences of its failure post-earthquake functional needs historical value
or economic importance (as given in Table ndash 82)
Table ndash 82 Importance Factors I [IS 1893 (Part 1) 2002]
S
No
Structure Importance
Factor
(i) Important service and community buildings such as hospitals schools
monumental structures emergency buildings like telephone exchange
television stations radio stations railway stations fire station buildings
large community halls like cinemas assembly halls and subway stations
power stations
15
(ii) AU other buildings 10
Note
1 The design engineer may choose values of importance factor I greater than those
mentioned above
2 Buildings not covered in S No (i) and (ii) above may be designed for higher value of I
depending on economy strategy considerations like multi-storey buildings having
several residential units
3 This does not apply to temporary structures like excavations scaffolding etc of short
duration
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R = Response Reduction Factor
To make normal buildings economical design code allows some damage for reducing the
cost of construction This philosophy is introduced with the help of Response reduction
factor R
The ratio (IR) shall not be greater than 10
Depending on the perceived seismic damage performance of the structure by ductile or brittle
deformations the values of R1)
for buildings are given in Table ndash 83 below
Table ndash 83 Response Reduction Factor1)
R for Building Systems [IS 1893 (Part 1) 2002]
S No Lateral Load Resisting System R Building Frame Systems (i) Ordinary RC moment-resisting frame ( OMRF )
2) 30
(ii) Special RC moment-resisting frame ( SMRF )3)
50 (iii) Steel frame with
a) Concentric braces 40 b) Eccentric braces 50
(iv) Steel moment resisting frame designed as per SP 6 (6) 50 Building with Shear Walls
4)
(v) Load bearing masonry wall buildings5)
a) Unreinforced 15 b) Reinforced with horizontal RC bands 25 c) Reinforced with horizontal RC bands and vertical bars at cornersof
rooms and jambs of openings 30
(vi) Ordinary reinforced concrete shear walls6)
30 (vii) Ductile shear walls
7) 40
Buildings with Dual Systems8)
(viii) Ordinary shear wall with OMRF 30 (ix) Ordinary shear wall with SMRF 40 (x) Ductile shear wall with OMRF 45 (xi) Ductile shear wall with SMRF 50 1) The values of response reduction factor are to be used for buildings with lateral load resisting
elements and not just for the lateral load resisting elements built in isolation 2) OMRF (Ordinary Moment-Resisting Frame) are those designed and detailed as per IS 456 or
IS 800 but not meeting ductile detailing requirement as per IS 13920 or SP 6 (6) respectively 3) SMRF (Special Moment-Resisting Frame) defined in 4152
As per 4152 SMRF is a moment-resisting frame specially detailed to provide ductile behaviour and comply with the requirements given in IS 4326 or IS 13920 or SP 6 (6)
4) Buildings with shear walls also include buildings having shear walls and frames but where a) frames are not designed to carry lateral loads or b) frames are designed to carry lateral loads but do not fulfil the requirements of lsquodual
systemsrsquo 5) Reinforcement should be as per IS 4326 6) Prohibited in zones IV and V 7) Ductile shear walls are those designed and detailed as per IS 13920 8) Buildings with dual systems consist of shear walls ( or braced frames ) and moment resisting
frames such that a) the two systems are designed to resist the total design force in proportion to their lateral
stiffness considering the interaction of the dual system at all floor levels and b) the moment resisting frames are designed to independently resist at least 25 percent of the
design seismic base shear
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Sag = Average Response Acceleration Coefficient
Net shaking of a building is a combined effect of the energy carried by the earthquake at
different frequencies and the natural period (T) of the building Code reflects this by
introducing a structural flexibility factor (Sag) also termed as Design Acceleration
Coefficient
Design Acceleration Coefficient (Sag) corresponding to 5 damping for different soil
types normalized to Peak Ground Acceleration (PAG) corresponding to natural period (T)
of structure considering soil structure interaction given by Fig 81 and associated expression
given below
Table ndash 84 gives multiplying factors for obtaining spectral values for various other damping
Table ndash 84 Multiplying Factors for Obtaining Values for Other Damping [IS 1893 (Part 1) 2002]
Damping () 0 2 5 7 10 15 20 25 30
Factors 320 140 100 090 080 070 060 055 050
85 को पन की मौतलक पराकतिक अवतध Fundamental Natural Period of Vibration
The approximate fundamental natural period of vibration (Ta)in seconds of a moment-resisting
frame building without brick infill panels may be estimated by the empirical expression
Ta = 0075 h075
for RC frame building
= 0085 h075
for steel frame building
Where h = Height of building in m This excludes the basement storeys where
basement walls are connected with the ground floor deck or fitted between
the building columns But it includes the basement storeys when they are
not so connected
Fig 81 Response Spectra for Rock and Soil Sitesfor5 Damping [IS 1893 (Part 1) 2002]
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53
The approximate fundamental natural period of vibration (Ta) in seconds of all other buildings
including moment-resisting frame buildings with brick infill panels may be estimated by the
empirical expression
Where h = Height of building in m as defined above
d = Base dimension of the building at the plinth level in m along the
considered direction of the lateral force
86 तिजाइन पारशय बल Design Lateral Force
The total design lateral force or design seismic base shear (VB) along any principal direction shall
be determined by the following expression
Where Ah= Design horizontal acceleration spectrum value as per 642 using the
fundamental natural period Ta as per 76 in the considered direction of
vibration and
W= Seismic weight of the building
The design lateral force shall first be computed for the building as a whole This design lateral
force shall then be distributed to the various floor levels
The overall design seismic force thus obtained at each floor level shall then be distributed to
individual lateral load resisting elements depending on the floor diaphragm action
87 तिजाइन बल का तविरण Distribution of Design Force
871 Vertical Distribution of Base Shear to Different Floor Levels
The Design Seismic Base Shear (VB) as computed above shall be distributed along the height of
the building as per the following expression
Where
Qi= Design lateral force at floor i
Wi = Seismic weight of floor i
hi = Height of floor i measured from base and
n= Number of storeys in the building is the number of levels at which the masses are
located
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872 Distribution of Horizontal Design Lateral Force to Different Lateral Force Resisting
Elements
1 In case of buildings whose floors are capable of providing rigid horizontal diaphragm
action the total shear in any horizontal plane shall be distributed to the various vertical
elements of lateral force resisting system assuming the floors to be infinitely rigid in the
horizontal plane
2 In case of building whose floor diaphragms cannot be treated as infinitely rigid in their
own plane the lateral shear at each floor shall be distributed to the vertical elements
resisting the lateral forces considering the in-plane flexibility of the diaphragms
Notes
1 A floor diaphragm shall be considered to be flexible if it deforms such that the maximum
lateral displacement measured from the chord of the deformed shape at any point of the
diaphragm is more than 15 times the average displacement of the entire diaphragm
2 Reinforced concrete monolithic slab-beam floors or those consisting of prefabricated
precast elements with topping reinforced screed can be taken rigid diaphragms
88 तिजाइन उदािरण Design Example ndash To determine Base Shear and its distribution
along Height of Building
Exercise ndash 1 Determine the total base shear as per IS 1893(Part 1)2002 and distribute the base
shear along the height of building to be used as school building in Bhuj Gujrat and founded on
Medium Soil Basic parameters for design of building are as follows
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55
ELEVATION
Solution
Basic Data
Following basic data is considered for analysis
i) Grade of Concrete M-25
ii) Grade of Steel Fe ndash 415 Tor Steel
iii) Density of Concrete 25 KNm3
iv) Density of Brick Wall 20 KNm3
v) Live Load for Roof 15 KNm2
vi) Live Load for Floor 50 KNm2
vii) Slab Thickness 150 mm
viii) Beam Size
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56
(a) 500 m Span 250 mm X 600 mm
(b) 400 m Span 250 mm X 550 mm
(c) 200 m Span 250 mm X 400 mm
ix) Column Size
(a) For 500 m Span 300 mm X 600 mm
(b) For 200 m Span 300 mm X 500 mm
Load Calculations
1 Dead Load Building is of G+4 Storeys
Approximate Covered Area of Building on GF = 30 X 8 = 240 m2
Approximate Covered Area of 1st 2
nd 3
rd amp 4
th Floor = 240 m
2
Total Floor Area = 5 X 240 = 1200 m2
Roof Area = 1 X 240 = 240 m2
(I) Slab
Self Wt of Slab = 015 X 25 = 375 KNm2
Wt of Floor Finish = 125 KNm2
------------------------------
Total = 500 KNm2
Dead Load of Slab per Floor = 240 X 5 = 1200 KN
Dead Load of Slab on Roof = 240 X 5 = 1200 KN
(II) Beam
Wt per m of 250 X 600 mm beam = 025 X 060 X 25 = 375 KNm
Wt per m of 250 X 550 mm beam = 025 X 055 X 25 = 344 KNm
Wt per m of 250 X 400 mm beam = 025 X 040 X 25 = 250 KNm
Weight of Beam per Floor
= (2 X 30 X 375) + (4 X 6 + 30) X 344 + (2 X 6 X 250)
= 225 + 18576 + 30 = 44076 KN [Say 44100 KN]
(III) Column
Wt per m of 300 X 600 mm column = 030 X 060 X 25 = 450 KNm
Wt per m of 300 X 500 mm column = 030 X 050 X 25 = 375 KNm
Weight of Column per Floor
= (12 X 3 X 450) + (6 X 3 X 375)
= 162 + 6750 = 22950 KN [Say 23000 KN]
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57
Walls
250 mm thick wall (including plaster) are provided Assuming 20 opening in the
wall ndash
Wt of Wall per m = 025 X 080 X 20 X 250
Wall Thickness Reduction Density Clear Height
= 1000 KNm
Wt of Parapet Wall per m = 0125 X 20 X 100 = 250 KNm
Wall Thickness Density Clear Height
Wt of Wall per Floor = 1000 X [30 X 3 + 2 X 2] = 940 KN
Wt of Wall at Roof = 250 X [30 X 2 + 8 X 2] = 190 KN
Total Dead Load ndash
(i) For Floor = Slab + Beam + Column + Wall
= 1200 + 441 + 230 + 940 = 2811 KN
(ii) For Roof = 1200 + 441 + 190 = 1831 KN
Slab Beam Parapet
2 Live Load Live Load on Floor = 40 KNm2
As per Table ndash 8 in Cl 731 of IS 1893 (Part 1)2002 ldquoage of Imposed Load to be
considered in Seismic Weight calculationrdquo
(i) Up to amp including 300 KNm2 = 25
(ii) Above 300 KNm2 = 50
Live Load on Floors to be = 200 KNm2 [ie 50 of 40 KNm
2]
considered for Earthquake Force
As per Cl 732 of IS 1893 (Part 1)2002 for calculating the design seismic force of the
structure the imposed load on roof need not be considered
Therefore Live Load on Roof = 000 KN
Seismic Weight due to Live Load
(i) For Floor = 240 X 2 = 480 KN
(ii) For Roof = 000 KN
3 Seismic Weight of Building
As per Cl 74 of IS 1893 (Part 1)2002
(i) For Floor = DL of Floor + LL on Floor
= 2811 + 480 = 3291 KN
(ii) For Roof = 1831 + 000 = 1831 KN
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58
Total Seismic Weight of Building = 5 X 3291 + 1 X 1831
W = 18286 KN
4 Determination of Base Shear
As per Cl 75 of IS 1893 (Part 1)2002 VB = Ah W
Where
VB = Base Shear
Ah = Design Horizontal Acceleration Spectrum
=
W = Seismic Wt of Building
Total height of Building above Ground Level = 1500 m
As per Cl 76 of IS 1893 (Part 1)2002 Fundamental Natural Period of Vibration for RC
Frame Building is
Ta = 0075 h075
= 0075 (15)075
= 0572 Sec
Average Response Acceleration Coefficient = 25
for 5 damping and Type II soil
Bhuj Gujrat is in Seismic Zone V
As per Table ndash 2 of IS 1893 (Part 1)2002
Zone Factor Z = 036
As per Table ndash 6 of IS 1893 (Part 1)2002
Impedance Factor I = 150
As per Table ndash 7 of IS 1893 (Part 1)2002
Response Reduction Factor for Ordinary R = 300
RC Moment-resisting Frame (OMRF) Building
Ah =
= (0362) X (1530) X (25)
= 0225
Base Shear VB = Ah W
= 0225 X 18286
= 411435 KN [Say 411400 KN]
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5 Vertical Distribution of Base Shear to Different Floors Levels
As per Cl 771 of IS 1893 (Part 1)2002
Where
Qi= Design lateral force at floor i
Wi = Seismic weight of floor i
hi = Height of floor i measured from base and
n= Number of storeys in the building is the number of levels at which the masses are
located
VB = 4114 KN
Storey
No
Mass
No
Wi hi Wi hi2
f =
Qi = VB x f
(KN)
Vi
(KN)
Roof 1 1831 18 593244 0268 1103 1103
4th
Floor 2 3291 15 740475 0333 1370 2473
3rd
Floor 3 3291 12 473904 0213 876 3349
2nd
Floor 4 3291 9 266571 0120 494 3843
1st Floor 5 3291 6 118476 0053 218 4061
Ground 6 3291 3 29619 0013 53 4114
= 2222289
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60
अधयाय Chapter ndash 9
ढााचागि सोरचना का तनमायण Construction of Framed Structure
91 गरतवाकषयण लोतिोग और भको प लोतिोग म आर सी तबकडोग का वयविार Behaviour of RC
Building in Gravity Loading and Earthquake Loading
In recent times reinforced concrete buildings have become common in India particularly in
towns and cities A typical RC building consists of horizontal members (beams and slabs) and
vertical members (columns and walls) The system is supported by foundations that rest on
ground The RC frame participates in resisting the gravity and earthquake forces as illustrated in
Fig 91
Gravity Loading
1 Load due to self weight and contents on buildings cause RC frames to bend resulting in
stretching and shortening at various locations
2 Tension is generated at surfaces that stretch
and compression at those that shorten
3 Under gravity loads tension in the beams is
at the bottom surface of the beam in the
central location and is at the top surface at
the ends
Earthquake Loading
1 It causes tension on beam and column faces
at locations different from those under
gravity loading the relative levels of this
tension (in technical terms bending
moment) generated in members are shown
in Figure
2 The level of bending moment due to
earthquake loading depends on severity of
shaking and can exceed that due to gravity
loading
3 Under strong earthquake shaking the beam
ends can develop tension on either of the
top and bottom faces
4 Since concrete cannot carry this tension
steel bars are required on both faces of
beams to resist reversals of bending
moment
5 Similarly steel bars are required on all faces of columns too
Fig 91 Earthquake shaking reverses tension and
compression in members ndash reinforcement is
required on both faces of members
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92 परबतलि को करीट इमारिो ो पर कषतिज भको प का परभाव Effect of Horizontal Earthquake Force
on RC Buildings
Earthquake shaking generates inertia forces in the building which are proportional to the
building mass Since most of the building mass is present at floor levels earthquake-induced
inertia forces primarily develop at the floor
levels These forces travel downwards -
through slab and beams to columns and walls
and then to the foundations from where they
are dispersed to the ground (Fig 92)
As inertia forces accumulate downwards from
the top of the building the columns and walls
at lower storeys experience higher earthquake-
induced forces and are therefore designed to be
stronger than those in storeys above
93 कषमिा तिजाइन सोकलपना Capacity Design Concept
(i) Let us take two bars of same length amp Cross-sectional area
1st bar ndash Made up of Brittle Material
2nd
bar ndash Made up of Ductile Material
(ii) Pull both the bars until they break
(iii) Plot the graph of bar force F versus bar
elongation Graph will be as given in Fig
93
(iv) It is observed that ndash
a) Brittle bar breaks suddenly on reaching its
maximum strength at a relatively small
elongation
b) Ductile bar elongates by a large amount
before it breaks
Materials used in building construction are steel
masonry and concrete Steel is ductile material
while masonry and concrete are brittle material
Capacity design concept ensures that the brittle
element will remain elastic at all loads prior to the
failure of ductile element Thus brittle mode of
failure ie sudden failure has been prevented
Fig 92 Total horizontal earthquake force in a
building increase downwards along its height
Fig 93 Tension Test on Materials ndash ductile
versus brittle materials
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The concept of capacity design is used to ensure post-yield ductile behaviour of a structure
having both ductile and brittle elements In this method the ductile elements are designed and
detailed for the design forces Then an upper-bound strength of the ductile elements is obtained
It is then expected that if the seismic force keeps increasing a point will come when these ductile
elements will reach their upper-bound strength and become plastic Clearly it is necessary to
ensure that even at that level of seismic force the brittle elements remain safe
94 लचीलापन और ऊजाय का अपवयय Ductility and Energy Dissipation
From strength point of view overdesigned structures need not necessarily demonstrate good
ductility By ductility of Moment Resisting Frames (MRF) one refers to the capacity of the
structure and its elements to undergo large deformations without loosing either strength or
stiffness It is important for a building in a seismic zone to be resilient ie absorb the shock from
the ground and dissipate this energy uniformly throughout the structure
In MRFs the dissipation of the input seismic energy takes place in the form of flexural yielding
and resulting in the formation of plastic moment hinges Due to cyclic nature of the flexural
effects both positive and negative plastic moment hinges may be formed
95 मजबि सतोभ ndash कमजोर बीम फलोसफ़ी lsquoStrong Column ndash Weak Beamrsquo Philosophy
Because beams are usually capable of developing large ductility than columns which are
subjected to significant compressive loads many building frames are designed based on the
lsquostrong column ndash weak beamrsquo philosophy Figure shows that for a frame designed according to
the lsquostrong column ndash weak beamrsquo philosophy to form a failure mechanism many more plastic
hinges have to be formed than a
frame designed according to the
ldquoweak column ndash strong beamrsquo
philosophy The frames designed
by the former approach dissipate
greater energy before failure
When this strategy is adopted in
design damage is likely to occur
first in beams When beams are
detailed properly to have large
ductility the building as a whole
can deform by large amounts
despite progressive damage caused
due to consequent yielding of
beams
Note If columns are made weaker they suffer severe local damage at the top and bottom of a
particular storey This localized damage can lead to collapse of a building although columns at
storeys above remain almost undamaged (Fig 94)
Fig 94 Two distinct designs of buildings that result in different
earthquake performancesndashcolumns should be stronger than beams
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For a building to remain safe during earthquake shaking columns (which receive forces from
beams) should be stronger than beams and foundations (which receive forces from columns)
should be stronger than columns
96 कठोर िायाफराम तकरया Rigid Diaphragm Action
When beams bend in the vertical direction during earthquakes these thin slabs bend along with them And when beams move with columns in the horizontal direction the slab usually forces the beams to move together with it In most buildings the geometric distortion of the slab is negligible in the horizontal plane this behaviour is known as the rigid diaphragm action This aspect must be considered during design (Fig 95)
97 सॉफट सटोरी तबकडोग क साथ ndash ओपन गराउोि सटोरी तबकडोग जो तक भको प क समय कमजोर िोिी ि
Building with Soft storey ndash Open Ground Storey Building that is vulnerable in
Earthquake
The buildings that have been constructed in recent times with a special feature - the ground storey is left open for the purpose of parking ie columns in the ground storey do not have any partition walls (of either masonry or RC) between them are called open ground storey buildings or buildings on stilts
An open ground storey building (Fig 96) having only columns in the ground storey and both partition walls and columns in the upper storeys have two distinct characteristics namely
(a) It is relatively flexible in the ground storey ie the relative horizontal displacement it undergoes in the ground storey is much larger than what each of the storeys above it does This flexible ground storey is also called soft storey
(b) It is relatively weak in ground storey ie
the total horizontal earthquake force it can carry in the ground storey is significantly smaller than what each of the storeys above it can carry Thus the open ground storey may also be a weak storey
Fig 95 Floor bends with the beam but moves all
columns at that level together
Fig 96 Upper storeys of open ground storey building
move together as a single block ndash such buildings are
like inverted pendulums
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The collapse of more than a hundred RC frame buildings with open ground storeys at
Ahmedabad (~225km away from epicenter) during the 2001 Bhuj earthquake has emphasized
that such buildings are extremely vulnerable under earthquake shaking
After the collapses of RC buildings in 2001 Bhuj earthquake the Indian Seismic Code IS 1893
(Part 1) 2002 has included special design provisions related to soft storey buildings
Firstly it specifies when a building should be considered as a soft and a weak storey building
Secondly it specifies higher design forces for the soft storey as compared to the rest of the
structure
The Code suggests that the forces in the columns
beams and shear walls (if any) under the action of
seismic loads specified in the code may be
obtained by considering the bare frame building
(without any infills) However beams and
columns in the open ground storey are required to
be designed for 25 times the forces obtained
from this bare frame analysis (Fig 97)
For all new RC frame buildings the best option is
to avoid such sudden and large decrease in stiffness
andor strength in any storey it would be ideal to
build walls (either masonry or RC walls) in the
ground storey also Designers can avoid dangerous
effects of flexible and weak ground storeys by
ensuring that too many walls are not discontinued
in the ground storey ie the drop in stiffness and
strength in the ground storey level is not abrupt due
to the absence of infill walls (Fig 98)
The existing open ground storey buildings need to be strengthened suitably so as to prevent them
from collapsing during strong earthquake shaking The owners should seek the services of
qualified structural engineers who are able to suggest appropriate solutions to increase seismic
safety of these buildings
971 भरी हई दीवार In-Fill Walls
When columns receive horizontal forces at floor
levels they try to move in the horizontal direction
but masonry walls tend to resist this movement
Due to their heavy weight and thickness these
walls attract rather large horizontal forces
However since masonry is a brittle material these
walls develop cracks once their ability to carry
horizontal load is exceeded Thus infill walls act
like sacrificial fuses in buildings they develop
Fig 99 Infill walls move together with the
columns under earthquake shaking
Fig 97 Open ground storey building ndashassumptions
made in current design practice are not consistent
with the actual structure
Fig 98 Avoiding open ground storey problem ndash
continuity of walls in ground storey is preferred
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65
cracks under severe ground shaking but help share the load of the beams and columns until
cracking Earthquake performance of infill walls is enhanced by mortars of good strength
making proper masonry courses and proper packing of gaps between RC frame and masonry
infill walls (Fig 99)
98 भको प क दौरान लघ कॉलम वाली इमारिो ो का वयविार Behavior of Buildings with Short
Columns during Earthquakes
During past earthquakes reinforced concrete (RC) frame buildings that have columns of different heights within one storey suffered more damage in the shorter columns as compared to taller columns in the same storey
Two examples of buildings with short columns are shown in Fig 910 ndash (a) buildings on a sloping ground and (b) buildings with a mezzanine floor
Poor behaviour of short columns is due to the fact that in an earthquake a tall column and a short column of same cross-section move horizontally by same amount
However the short column is stiffer as compared
to the tall column and it attracts larger earthquake
force Stiffness of a column means resistance to
deformation ndash the larger is the stiffness larger is
the force required to deform it If a short column is
not adequately designed for such a large force it
can suffer significant damage during an
earthquake This behaviour is called Short Column
Effect (Fig 911)
In new buildings short column effect should be
avoided to the extent possible during architectural
design stage itself When it is not possible to avoid
short columns this effect must be addressed in
structural design The IS13920-1993for ductile
detailing of RC structures requires special
confining reinforcement to be provided over the
full height of columns that are likely to sustain
short column effect
Fig 910 Buildings with short columns ndash two
explicit examples of common occurrences
Fig 911 Short columns are stiffer and attract larger
forces during earthquakes ndash this must be accounted
for in design
Fig 912 Details of reinforcement in a building with
short column effect in some columns ndashadditional
special requirements are given in IS13920- 1993 for
the short columns
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66
The special confining reinforcement (ie closely spaced closed ties) must extend beyond the
short column into the columns vertically above and below by a certain distance as shown in
Fig 912
In existing buildings with short columns different retrofit solutions can be employed to avoid
damage in future earthquakes Where walls of partial height are present the simplest solution is
to close the openings by building a wall of full height ndash this will eliminate the short column
effect If that is not possible short columns need to be strengthened using one of the well
established retrofit techniques The retrofit solution should be designed by a qualified structural
engineer with requisite background
99 भको प परतिरोधी इमारिो ो की लचीलापन आवशयकिाएा Ductility requirements of
Earthquake Resistant Buildings
The primary members of structure such as beams and columns are subjected to stress reversals
from earthquake loads The reinforcement provided shall cater to the needs of reversal of
moments in beams and columns and at their junctions
Earthquake motion often induces forces large enough to cause inelastic deformations in the
structure If the structure is brittle sudden failure could occur But if the structure is made to
behave ductile it will be able to sustain the earthquake effects better with some deflection larger
than the yield deflection by absorption of energy Therefore besides the design for strength of
the frame ductility is also required as an essential element for safety from sudden collapse during
severe shocks
The ductility requirements will be deemed to be satisfied if the conditions given as in the
following are achieved
1 For all buildings which are more than 3 storeys in height the minimum grade of concrete
shall be M20 ( fck = 20 MPa )
2 Steel reinforcements of grade Fe 415 (IS 1786 1985) or less only shall be used
However high strength deformed steel bars produced by the thermo-mechanical treatment
process of grades Fe 500 and Fe 550 having elongation more than 145 percent and conforming
to other requirements of IS 1786 1985 may also be used for the reinforcement
910 बीम तजनह आर सी इमारिो ो म भको प बलो ो का तवरोध करन क तलए िाला जािा ि Beams that
are required to resist Earthquake Forces in RC Buildings
In RC buildings the vertical and horizontal members (ie the columns and beams) are built
integrally with each other Thus under the action of loads they act together as a frame
transferring forces from one to another
Beams in RC buildings have two sets of steel reinforcement (Fig 913) namely
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(a) long straight bars (called longitudinal bars)
placed along its length and
(b) closed loops of small diameter steel bars (called
stirrups)placed vertically at regular intervals
along its full length
Beams sustain two basic types of failures namely
(i) Flexural (or Bending) Failure
As the beam sags under increased loading it can
fail in two possible ways (Fig 914)
If relatively more steel is present on the tension
face concrete crushes in compression this is
a brittle failure and is therefore undesirable
If relatively less steel is present on the
tension face the steel yields first (it keeps
elongating but does not snap as steel has
ability to stretch large amounts before it
snaps and redistribution occurs in the beam
until eventually the concrete crushes in
compression this is a ductile failure and
hence is desirable Thus more steel on
tension face is not necessarily desirable The
ductile failure is characterized with many
vertical cracks starting from the stretched
beam face and going towards its mid-depth
(ii) Shear Failure
A beam may also fail due to shearing action A shear crack is inclined at 45deg to the horizontal it
develops at mid-depth near the support and grows towards the top and bottom faces Closed loop
stirrups are provided to avoid such shearing action Shear damage occurs when the area of these
stirrups is insufficient Shear failure is brittle and therefore shear failure must be avoided in the
design of RC beams
Longitudinal bars are provided to resist flexural
cracking on the side of the beam that stretches
Since both top and bottom faces stretch during
strong earthquake shaking longitudinal steel bars
are required on both faces at the ends and on the
bottom face at mid-length (Fig 915)
Fig 914 Two types of damage in a beam flexure
damage is preferred Longitudinal bars resist the
tension forces due to bending while vertical stirrups
resist shear forces
Fig 913 Steel reinforcement in beams ndash stirrups
prevent longitudinal bars from bending outwards
Fig 915 Location and amount of longitudinal steel
bars in beams ndash these resist tension due to flexure
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Designing a beam involves the selection of its material properties (ie grades of steel bars
and concrete) and shape and size these are usually selected as a part of an overall design
strategy of the whole building
The amount and distribution of steel to be provided in the beam must be determined by
performing design calculations as per IS 456-2000 and IS 13920-1993
911 फलकसचरल ममबसय क तलए सामानय आवशयकिाएा General Requirements for Flexural
Members
These members shall satisfy the following requirements
The member shall preferably have a width-to-depth ratio of more than 03
The width of the member shall not be less than 200 mm
The depth D of the member shall preferably be not more than 14 of the clear span
The factored axial stress on the member under earthquake loading shall not exceed 01fck
9111 अनदधयय सदढीकरण Longitudinal Reinforcement
a) The top as well as bottom reinforcement shall consist of at least two bars throughout the
member length
b) The tension steel ratio on any face at any section shall not be less than ρmin = 024 where fck
and fy are in MPa
The positive steel at a joint face must be at least equal to half the negative steel at that face
The steel provided at each of the top and bottom face of the member at any section along its
length shall be at least equal to one-fourth of the maximum negative moment steel provided
at the face of either joint It may be clarified that
redistribution of moments permitted in IS 456
1978 (clause 361) will be used only for vertical
load moments and not for lateral load moments
In an external joint both the top and the bottom
bars of the beam shall be provided with anchorage
length beyond the inner face of the column equal
to the development length in tension plus 10 times
the bar diameter minus the allowance for 90 degree
bend(s) (as shown in Fig 916) In an internal joint
both face bars of the beam shall be taken
continuously through the column
Fig 916 Anchorage of Beam Bars in an External Joint (IS 13920 1993)
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9112 अनदधयय सदढीकरण की सपलाइतसोग Splicing of longitudinal reinforcement
The longitudinal bars shall be spliced only if hoops are
provided over the entire splice length at a spacing not
exceeding 150 mm (as shown in Fig 917) The lap length
shall not be less than the bar development length in tension
Lap splices shall not be provided (a) within a joint (b)
within a distance of 2d from joint face and (c) within a
quarter length of the member where flexural yielding may
generally occur under the effect of earthquake forces Not
more than 50 percent of the bars shall be spliced at one
section
Use of welded splices and mechanical connections may also be made as per 25252 of
IS 456-1978 However not more than half the reinforcement shall be spliced at a section
where flexural yielding may take place
9113 वब सदढीकरण Web Reinforcement
Web reinforcement shall consist of vertical hoops A vertical hoop is a closed stirrup having a
135deg hook with a 10 diameter extension (but
not lt 75 mm) at each end that is embedded
in the confined core [as shown in (a) of
Fig 918] In compelling circumstances it
may also be made up of two pieces of
reinforcement a U-stirrup with a 135deg hook
and a 10 diameter extension (but not lt 75
mm) at each end embedded in the confined
core and a crosstie [as shown in (b) of Fig
918] A crosstie is a bar having a 135deg hook
with a 10 diameter extension (but not lt 75
mm) at each end The hooks shall engage
peripheral longitudinal bars
912 कॉलम तजनह आर सी इमारिो ो म भको प बलो ो का तवरोध करन क तलए िाला जािा ि Columns that are required to resist Earthquake Forces in RC Buildings
Columns the vertical members in RC buildings contain two types of steel reinforcement
namely
(a) long straight bars (called longitudinal bars) placed vertically along the length and
(b) closed loops of smaller diameter steel bars (called transverse ties) placed horizontally at
regular intervals along its full length
Fig 917 Lap Splice in Beam
(IS 13920 1993)
Fig 918 Beam Web Reinforcement (IS 13920 1993)
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Columns can sustain two types of damage namely axial-flexural (or combined compression-
bending) failure and shear failure Shear damage is brittle and must be avoided in columns by
providing transverse ties at close spacing
Closely spaced horizontal closed ties (Fig 919)
help in three ways namely
(i) they carry the horizontal shear forces
induced by earthquakes and thereby resist
diagonal shear cracks
(ii) they hold together the vertical bars and
prevent them from excessively bending
outwards(in technical terms this bending
phenomenon is called buckling) and
(iii) they contain the concrete in the column
within the closed loops The ends of the
ties must be bent as 135deg hooks Such hook
ends prevent opening of loops and
consequently bulging of concrete and
buckling of vertical bars
Construction drawings with clear details of closed ties are helpful in the effective implementation
at construction site In columns where the spacing between the corner bars exceeds 300mm the
Indian Standard prescribes additional links with 180deg hook ends for ties to be effective in holding
the concrete in its place and to prevent the buckling of vertical bars These links need to go
around both vertical bars and horizontal closed ties (Fig 920) special care is required to
implement this properly at site
Designing a column involves selection of
materials to be used (ie grades of concrete and
steel bars) choosing shape and size of the cross-
section and calculating amount and distribution
of steel reinforcement The first two aspects are
part of the overall design strategy of the whole
building The IS 13920 1993 requires columns
to be at least 300mm wide A column width of up
to 200 mm is allowed if unsupported length is less
than 4m and beam length is less than 5m
Columns that are required to resist earthquake
forces must be designed to prevent shear failure
by a skillful selection of reinforcement
Fig 919 Steel reinforcement in columns ndash closed ties
at close spacing improve the performance of column
under strong earthquake shaking
Fig 920 Extra links are required to keep the
concrete in place ndash 180deg links are necessary to
prevent the135deg tie from bulging outwards
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913 एकसीयल लोिि मबसय क तलए सामानय आवशयकिाएा General Requirements for Axial
Loaded Members
These requirements apply to frame members which have a factored axial stress in excess of
01 fck under the effect of earthquake forces
The minimum dimension of the member shall not be less than 200 mm However in frames
which have beams with centre to centre span exceeding 5 m or columns of unsupported
length exceeding 4 m the shortest dimension of the column shall not be less than 300 mm
The ratio of the shortest cross sectional dimension to the perpendicular dimension shall
preferably not be less than 04
9131 अनदधयय सदढीकरण Longitudinal Reinforcement
Lap splices shall be provided only in the central half
of the member length It should be proportioned as a
tension splice Hoops shall be provided over the
entire splice length at spacing not exceeding 150
mm centre to centre Not more than 50 percent of
the bars shall be spliced at one section
Any area of a column that extends more than 100
mm beyond the confined core due to architectural
requirements shall be detailed in the following
manner
a) In case the contribution of this area to strength
has been considered then it will have the minimum longitudinal and transverse
reinforcement as per IS 13920 1993
b) However if this area has been treated as non-structural the minimum reinforcement
requirements shall be governed by IS 456 1978 provisions minimum longitudinal and
transverse reinforcement as per IS 456 1978 (as shown in Fig 921)
9132 अनपरसथ सदढीकरण Transverse Reinforcement
Transverse reinforcement for circular columns shall consist of spiral or circular hoops In
rectangular columns rectangular hoops may be used A rectangular hoop is a closed stirrup
having a 135deg hook with a 10 diameter extension (but not lt 75 mm) at each end that is
embedded in the confined core [as shown in (A) of Fig 922]
Fig 921 Reinforcement requirement for Column with more than 100 mm projection beyond core(IS 13920 1993)
Fig 922 Transverse Reinforcement in Column (IS 13920 1993)
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The parallel legs of rectangular hoop shall be spaced not more than 300 mm centre to centre
If the length of any side of the hoop exceeds 300 mm a crosstie shall be provided [as shown
in (B) of Fig 922] Alternatively a pair of overlapping hoops may be provided within the
column [as shown in (C) of Fig 922] The hooks shall engage peripheral longitudinal bars
The spacing of hoops shall not exceed half the least lateral dimension of the column except
where special confining reinforcement is provided as per Para 915 below
914 बीम-कॉलम जोड़ जो आर सी भवनो ो म भको प बलो ो का तवरोध करि ि Beam-Column Joints
that resist Earthquakes Forces in RC Buildings
In RC buildings portions of columns that are
common to beams at their intersections are
called beam column joints (Fig 923) The
joints have limited force carrying capacity
When forces larger than these are applied
during earthquakes joints are severely
damaged Repairing damaged joints is
difficult and so damage must be avoided
Thus beam-column joints must be designed
to resist earthquake effects
Under earthquake shaking the beams adjoining a joint are subjected to moments in the same
(clockwise or counter-clockwise) direction
Under these moments the top bars in the
beam-column joint are pulled in one
direction and the bottom ones in the
opposite direction These forces are
balanced by bond stress developed between
concrete and steel in the joint region
(Fig 924)
If the column is not wide enough or if the
strength of concrete in the joint is low there
is insufficient grip of concrete on the steel
bars In such circumstances the bar slips
inside the joint region and beams loose
their capacity to carry load Further under
the action of the above pull-push forces at top and bottom ends joints undergo geometric
distortion one diagonal length of the joint elongates and the other compresses
If the column cross-sectional size is insufficient the concrete in the joint develops diagonal
cracks
Fig 923 Beam-Column Joints are critical parts of a
building ndash they need to be designed
Fig924 Pull-push forces on joints cause two
problems ndash these result in irreparable damage in joints
under strong seismic shaking
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9141 बीम-कॉलम जोड़ मजबि करन क तलए सामानय आवशयकिाएा General Requirements
for Reinforcing the Beam-Column Joint
Diagonal cracking and crushing of concrete in joint
region should be prevented to ensure good
earthquake performance of RC frame buildings
(Fig 925)
Using large column sizes is the most effective
way of achieving this
In addition closely spaced closed-loop steel ties
are required around column bars to hold
together concrete in joint region and to resist
shear forces
Intermediate column bars also are effective in
confining the joint concrete and resisting
horizontal shear forces Providing closed-loop
ties in the joint requires some extra effort
IS 13920ndash1993 recommends continuing the
transverse loops around the column bars
through the joint region
In practice this is achieved by preparing the cage of
the reinforcement (both longitudinal bars and
stirrups) of all beams at a floor level to be prepared
on top of the beam formwork of that level and
lowered into the cage (Fig 926)
However this may not always be possible
particularly when the beams are long and the entire
reinforcement cage becomes heavy
The gripping of beam bars in the joint region is
improved first by using columns of reasonably
large cross-sectional size
The Indian Standard IS 13920-1993 requires building columns in seismic zones III IV and V to
be at least 300mm wide in each direction of the cross-section when they support beams that are
longer than 5m or when these columns are taller than 4m between floors (or beams)
In exterior joints where beams terminate at columns longitudinal beam bars need to be anchored
into the column to ensure proper gripping of bar in joint The length of anchorage for a bar of
grade Fe415 (characteristic tensile strength of 415MPa) is about 50 times its diameter This
Fig 925 Closed loop steel ties in beam-column
joints ndash such ties with 135deg hooks resist the ill
effects of distortion of joints
Fig 926 Providing horizontal ties in the joints ndash
three-stage procedure is required
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length is measured from the face of the column to the end of the bar anchored in the column
(Fig 927)
In columns of small widths and when beam
bars are of large diameter (Fig 928(a)) a
portion of beam top bar is embedded in the
column that is cast up to the soffit of the
beam and a part of it overhangs It is difficult
to hold such an overhanging beam top bar in
position while casting the column up to the
soffit of the beam Moreover the vertical
distance beyond the 90ordm bend in beam bars is
not very effective in providing anchorage
On the other hand if column width is large
beam bars may not extend below soffit of the
beam (Fig 928 (b)) Thus it is preferable to
have columns with sufficient width
In interior joints the beam bars (both top and
bottom) need to go through the joint without
any cut in the joint region Also these bars
must be placed within the column bars and
with no bends
915 तवशष सीतमि सदढीकरण Special Confining Reinforcement
This requirement shall be met with unless a
larger amount of transverse reinforcement is
required from shear strength considerations
Special confining reinforcement shall be
provided over a length lsquolorsquo from each
joint face towards mid span and on
either side of any section where flexural
yielding may occur under the effect of
earthquake forces (as shown in Fig 929)
The length lsquolorsquo shall not be less than
(a) larger lateral dimension of the
member at the section where yielding
occurs
(b) 16 of clear span of the member and
(c) 450 mm
Fig 929 Column and Joint Detailing (IS 13920 1993)
Fig 927 Anchorage of beam bars in exterior
joints ndash diagrams show elevation of joint region
Fig 928 Anchorage of beam bars in interior
jointsndash diagrams (a) and (b) show cross-sectional
views in plan of joint region
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When a column terminates into a footing or mat special confining reinforcement shall extend
at least 300 mm into the footing or mat (as shown in Fig 930)
When the calculated point of contra-flexure
under the effect of gravity and earthquake
loads is not within the middle half of the
member clear height special confining
reinforcement shall be provided over the full
height of the column
Columns supporting reactions from discontinued stiff members such as walls shall be
provided with special confining reinforcement over their full height (as shown in Fig 931)
This reinforcement shall also be placed above the discontinuity for at least the development
length of the largest longitudinal bar in the column Where the column is supported on a wall
this reinforcement shall be provided
over the full height of the column it
shall also be provided below the
discontinuity for the same development
length
Special confining reinforcement shall
be provided over the full height of a
column which has significant variation
in stiffness along its height This
variation in stiffness may result due to
the presence of bracing a mezzanine
floor or a RCC wall on either side of
the column that extends only over a part
of the column height (as shown in Fig
931)
916 तवशषिः भको पीय कषतर म किरनी दीवारो ो वाली इमारिो ो का तनमायण Construction of Buildings
with Shear Walls preferably in Seismic Regions
Reinforced concrete (RC) buildings often have vertical
plate-like RC walls called Shear Walls in addition to
slabs beams and columns These walls generally start
at foundation level and are continuous throughout the
building height Their thickness can be as low as
150mm or as high as 400mm in high rise buildings
Shear walls are usually provided along both length and
width of buildings Shear walls are like vertically-
oriented wide beams that carry earthquake loads
downwards to the foundation (Fig 932)
Fig 932 Reinforced concrete shear walls in
buildings ndash an excellent structural system for
earthquake resistance
Fig 930 Provision of Special confining reinforcement in Footings (IS 13920 1993)
Fig 931 Special Confining Reinforcement Requirement for
Columns under Discontinued Walls (IS 13920 1993)
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Properly designed and detailed buildings with shear walls have shown very good performance in
past earthquakes Shear walls in high seismic regions require special detailing Shear walls are
efficient both in terms of construction cost and effectiveness in minimizing earthquake damage
in structural and non-structural elements (like glass windows and building contents)
Shear walls provide large strength and
stiffness to buildings in the direction of their
orientation which significantly reduces lateral
sway of the building and thereby reduces
damage to structure and its contents
Since shear walls carry large horizontal
earthquake forces the overturning effects on
them are large Thus design of their
foundations requires special attention
Shear walls should be provided along
preferably both length and width However if
they are provided along only one direction a
proper grid of beams and columns in the
vertical plane (called a moment-resistant
frame) must be provided along the other
direction to resist strong earthquake effects
Door or window openings can be provided in shear walls but their size must be small to
ensure least interruption to force flow through walls
Shear walls in buildings must be symmetrically located in plan to reduce ill-effects of twist in
buildings (Fig 933)
Shear walls are more effective when located along exterior perimeter of the building ndash such a
layout increases resistance of the building to twisting
9161 िनय तिजाइन और किरनी दीवारो ो की जयातमति Ductile Design and Geometry of Shear
Walls
Shear walls are oblong in cross-section ie one dimension of the cross-section is much larger
than the other While rectangular cross-section is common L- and U-shaped sections are also
used Overall geometric proportions of the wall types and amount of reinforcement and
connection with remaining elements in the building help in improving the ductility of walls The
Indian Standard Ductile Detailing Code for RC members (IS13920-1993) provides special
design guidelines for ductile detailing of shear walls
917 इमपरवड़ तिजाइन रणनीतियाो Improved design strategies
9171 िातनकारक भको प परभाव स भवनो ो का सोरकषण Protection of Buildings from Damaging
Earthquake Effects
Conventional seismic design attempts to make buildings that do not collapse under strong
earthquake shaking but may sustain damage to non-structural elements (like glass facades) and
to some structural members in the building There are two basic technologies ndashBase Isolation
Fig 933 Shear walls must be symmetric in plan
layout ndash twist in buildings can be avoided
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Devices and Seismic Dampers which are used to protect buildings from damaging earthquake
effects
9172 आधार अलगाव Base Isolation
The idea behind base isolation is to detach (isolate) the building from the ground in such a way
that earthquake motions are not transmitted up through the building or at least greatly reduced
As illustrated in Fig 934 when the ground shakes the rollers freely roll but the building
above does not move Thus no force is
transferred to the building due to shaking of
the ground simply the building does not
experience the earthquake
As illustrated in Fig 935 if the same
building is rested on flexible pads that offer
resistance against lateral movements then
some effect of the ground shaking will be
transferred to the building above
As illustrated in Fig 936 if the flexible
pads are properly chosen the forces induced
by ground shaking can be a few times
smaller than that experienced by the
building built directly on ground namely a
fixed base building
9173 भको पी सोज Seismic Dampers
Seismic dampers are special devices introduced in the building to absorb the energy provided by
the ground motion to the building These dampers act like the hydraulic shock absorbers in cars ndash
much of the sudden jerks are absorbed in the hydraulic fluids and only little is transmitted above
to the chassis of the car
When seismic energy is transmitted through them dampers absorb part of it and thus damp the
motion of the building Commonly used types of seismic dampers (Fig 937) include
Fig 934 Hypothetical Building
Fig 935 Base Isolated Building
Fig 936 Fixed-Base Building
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Viscous dampers ndash Energy is absorbed by
silicone-based fluid passing between piston-
cylinder arrangement
Friction dampers ndash Energy is absorbed by
surfaces with friction between them rubbing
against each other
Yielding dampers ndash Energy is absorbed by
metallic components that yield
In India friction dampers have been provided in an
18-storey RC frame structure in Gurgaon
918 तिजाइन उदािरण Design Example ndash Beam Design of RC Frame with Ductile
Detailing
Exercise ndash 2 Beam Design of RC Frame Building as per Provision of IS 13920 1993 and IS
1893 (Part 1) 2002 Beam marked ABC is considered for Design
Fig 937 Seismic Energy Dissipation Devices
each device is suitable for a certain building
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ELEVATION
Solution
1 General Data Grade of Concrete = M 25
Grade of steel = Fe 415 Tor Steel
2 Load Combinations
As per Cl 63 of IS 1893 (Part 1) 2002 following are load combinations for Earthquake
Loading
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S No Load Combination DL LL EQ Remark
1 15 DL + 15 LL 15 15 ndash As per Table ndash 8
of IS 1893 (Part
1) 2002 2 12 (DL + LL
+ EQx) 15 025 or 050 +12
3 12 (DL + LL ndash EQx) 15 025 or 050 ndash12
4 12 (DL + LL + EQy) 15 025 or 050 +12
5 12 (DL + LL ndash EQy) 15 025 or 050 ndash12
6 15 (DL + EQx) 15 +15
7 15 (DL ndash EQx) 15 ndash15
8 15 (DL + EQy) 15 +15
9 15 (DL ndash EQy) 15 ndash15
10 09 DL + 15 EQx 15 +15
11 09 DL ndash 15 EQx 15 ndash15
12 09 DL + 15 EQy 15 +15
13 09 DL ndash 15 EQy 15 ndash15
EQx implies EQ Loading in X ndash direction amp EQy implies EQ Loading in Y ndash direction
where X amp Y are orthogonal directions and Z is vertical direction These load combinations
are for EQ Loading In practice Wind Load should also be considered in lieu of EQ Load
and critical of the two should be used in the design
In this exercise emphasis is to show calculations for ductile design amp detailing of building
elements subjected to Earthquake in the plan considered Beams parallel to Y ndash direction are
not significantly affected by Earthquake force in X ndash direction (except in case of highly
unsymmetrical building) and vice versa Beams parallel to Y ndash direction are designed for
Earthquake loading in Y ndash direction only
Torsion effect is not considered in this example
3 Force Data
For Beam AB force resultants for various load cases (ie DL LL amp EQ Load) from
Computer Analysis (or manually by any method of analysis) to illustrate the procedure of
design are tabulated below
Table ndash A Force resultants in beam AB for various load cases
Load Case Left End Centre Right End
Shear
(KN)
Moment
(KN-m)
Shear
(KN)
Moment
(KN-m)
Shear
(KN)
Moment
(KN-m)
DL ndash 51 ndash 37 4 32 59 ndash 56
LL ndash 14 ndash 12 1 11 16 ndash 16
EQY 79 209 79 11 79 ndash 119
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81
Table ndash B Force resultants in beam AB for different load combinations
Load Combinations Left End Centre Right End
Shear
(KN)
Moment
(KN-m)
Shear
(KN)
Moment
(KN-m)
Shear
(KN)
Moment
(KN-m)
15 DL + 15 LL 98 ndash 74 7 64 111 ndash 108
12 (DL + LL + EQy) 31 205 101 52 172 ndash 303
12 (DL + LL ndash EQy) 162 ndash 300 92 31 22 159
15 (DL + EQy) 44 261 127 61 209 ndash 372
15 (DL ndash EQy) 97 ndash 371 115 34 33 205
09 DL + 15 EQy 75 283 124 42 174 ndash 339
09 DL ndash 15 EQy 167 ndash 349 117 15 68 238
4 Various checks for Flexure Member
(i) Check for Axial Stress
As per Cl 611 of IS 13920 1993 flexural axial stress on the member under EQ loading
shall not exceed 01 fck
Factored Axial Force = 000 KN
Factored Axial Stress = 000 MPa lt 010 fck OK
Hence the member is to be designed as Flexure Member
(ii) Check for Member size
As per Cl 613 of IS 13920 1993 width of the member shall not be less than 200 mm
Width of the Beam B = 250 mm gt 200 mm OK
Depth of Beam D = 550 mm
As per Cl 612 member shall have a width to depth ratio of more than 03
BD = 250550 = 04545 gt 03 OK
As per Cl 614 depth of member shall preferably be not more than 14 of the clear span
ie (DL) lt 14 or (LD) gt4
Span = 4 m LD = 4000550 = 727 gt 4 OK
Check for Limiting Longitudinal Reinforcement
Nominal cover to meet Durability requirements as per = 30 mm
Table ndash 16 of IS 4562000 (Cl 2642) for Moderate Exposure
Effective depth for Moderate Exposure conditions = 550 ndash 30 ndash 20 ndash (202)
with 20 mm of bars in two layers = 490 mm
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82
As per Cl 621 (b) of IS 13920 1993 tension steel ratio on any face at any section shall not
be less than = (024 radic fck) fy
= (024 radic25) 415 = 0289 asymp 029
Min Reinforcement = (029100) X 250 X 490 = 356 mm2
Max Reinforcement 25 = (25100) X 250 X 490 = 3063 mm2
(iii) Design for Flexure
Design for Hogging Moment at support A
At end A from Table ndash B Mu = 371 KN-m
Therefore Mu bd2 = 371x10
6 (250 x 490 x 490) = 618
Referring to Table ndash 51 of SP ndash 16 for drsquod = 55490 = 011
We get Ast at top = 2013 Asc = 0866
Therefore Ast at top = (2013100) x 250 x 490
= 2466 mm2
gt 356 mm2 (Min Reinforcement)
lt 3063 mm2 (Max Reinforcement)
Asc at bottom = 0866
As per Cl 623 of IS 13290 1993 positive steel at a joint face must be at least equal to half
the ndashve steel at that face Therefore Asc at bottom must be at least 50 of Ast hence
Revised Asc = 20132 = 10065
Asc at bottom = (10065100) x 250 x 490
= 1233 mm2 gt 426 mm
2 (Min Reinforcement)
lt 3063 mm2 (Max Reinforcement)
Design for Sagging Moment at support A
Mu = 283 KN-m
The beam will be designed as T-beam The limiting capacity of the T-beam assuming xu lt Df
and xu lt xumax may be calculated as follows
Mu = 087 fy Ast d [1- (Ast fy bf d fck)] -------- (Eq ndash 1)
Where Df = Depth of Flange
= 150 mm
xu = Depth of Neutral Axis
xumax = Limiting value of Neutral Axis
= 048 d
= 048 X 490
= 23520 mm
bw = 250 mm
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83
bf = Width of Flange
= (L06) + bw + 6 Df or cc of beam
= (07 X 40006) + 250 + 6 X 150
= 467 + 250 + 900 = 1617 mm or 4000 mm cc
[Lower of two is to be adopted]
Substituting the values in Eq ndash 1 and solving the quadratic equation
283 X 106 = 087 X 415 Ast X 490 [1ndash (Ast X 415) (1617 X 490 X 25)]
= 1769145 Ast [1 ndash 2095 X 10-5
Ast]
283 X 106 = 1769145 Ast ndash 3706 Ast
2]
3706 Ast2 ndash 1769145 Ast + 283 X 10
6 = 0
Ast = [1769145 plusmn radic(17691452 ndash 4 X 3706 X 283 X 10
6)] 2 X 3706
= [1769145 plusmn radic(3129874 X 1010
ndash 4195192 X 106)] 2 X 3706
= (1769145 plusmn 16463155) 7412
Ast at bottom = 165717 mm2 gt 35600 mm
2
lt 306300 mm2 OK
It is necessary to check the design assumptions before finalizing the reinforcement
xu = (087 fy Ast) (036 fck bf)
= (087 X 415 X 1657) (036 X 25 X 1617)
= 4110 mm lt 150 mm OK
lt df
lt xumax = 048 X 490 = 235 mm OK
Ast = [1657(250X490)] X 100 = 1353
As per Cl 624 ldquoSteel provided at each of the top amp bottom face of the member at any one
section along its length shall be at least equal to 14th
of the maximum (-ve) moment steel
provided at the face of either joint
For Centre Mu = 64 KN-m
64 X 106 = 087 X 415 Ast X 490 [1ndash (Ast X 415) (1617 X 490 X 25)]
= 1769145 Ast [1 ndash 2095 X 10-5
Ast]
64 X 106 = 1769145 Ast ndash 3706 Ast
2]
3706 Ast2 ndash 1769145 Ast + 64 X 10
6 = 0
Ast = [1769145 plusmn radic(17691452 ndash 4 X 3706 X 64 X 10
6)] 2 X 3706
= 365 mm2
For Right Support Mu = 238 KN-m
238 X 106 = 087 X 415 Ast X 490 [1ndash (Ast X 415) (1617 X 490 X 25)]
= 1769145 Ast [1 ndash 2095 X 10-5
Ast]
238 X 106 = 1769145 Ast ndash 3706 Ast
2]
3706 Ast2 ndash 1769145 Ast + 238 X 10
6 = 0
Ast = [1769145 plusmn radic(17691452 ndash 4 X 3706 X 238 X 10
6)] 2 X 3706
= 1386 mm2
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(iv) Reinforcement Requirement
Top reinforcement is larger of Ast at top for hogging moment or Asc at top for sagging
moment ie 2466 mm2 or 968 mm
2 Hence provide 2466 mm
2 at top
Bottom reinforcement is larger of Asc at bottom for hogging moment or Ast at bottom for
sagging moment ie 1233 mm2 or 1936 mm
2 Hence provide 1936 mm
2 at bottom
Details of Reinforcement
Top Reinforcement
Beam AB Left End Centre Right End
Hogging Moment ndash 371 - ndash 371
Mu bd2 618 - 618
Ast at top 2013 - 2013
Asc at bottom 0866 lt 2013 2 =
10065 Hence
revised Asc = 10065
- 0866
Revised to
10065 as per Cl
623 of IS
139201993
Bottom Reinforcement
Sagging Moment 283 64 238
Ast at bottom Ast req = 1657 mm2
= 1353
gt 20132 =
10065 OK
Provide Ast at bottom
= 1353
Ast req = 365 mm2
= 0298
gt 029
gt 20134 =
0504 OK
As per Cl 624 of IS
139201993
Provide Ast at bottom
= 0504
Ast req = 1386 mm2
= 117
gt 029
gt 20132 =
10065
Provide Ast at
bottom = 117
Asc at top Asc req = 1657 2
= 829 mm2
= 0677
gt 029
gt 2013 4 =
0504 OK
Asc req = 05042
= 0252
gt 029 Provide MinAsc = 029
Asc req = 1657 2
= 829 mm2
= 0677
gt 029
gt 2013 4
= 0504
OK
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Summary of Reinforcement required
Beam Left End Centre Right End
Top = 2013
= 2466 mm2
Bottom = 1353
= 1658 mm2
Top = 0504
= 618 mm2
Bottom = 0504
= 618 mm2
Top = 2013
= 2466 mm2
Bottom = 10065
= 1233 mm2
Reinforcement provided
2 ndash 20Φ cont + 4 ndash 25Φ extra
Ast = 2592 mm2 (2116)
2 ndash 20Φ cont + 2 ndash 20Φ extra
+ 2 ndash 16 Φ
Ast = 1658 mm2 (1353)
2 ndash 20Φ cont
Ast = 628 mm2 (0512)
2 ndash 20Φ cont
Ast = 628 mm2 (0512)
2 ndash 20Φ cont
+ 4 ndash 25Φ extra
Top = 2592 mm2
2 ndash 20Φ cont
+ 2 ndash 20Φ extra + 2 ndash 16Φ
Ast = 1658 mm2 (1353)
Details of Reinforcement
Ld = Development Length in tension
db = Dia of bar
For Fe 415 steel and M25 grade concrete as per Table ndash 65 of SP ndash 16
For 25Φ bars 1007 + 10Φ - 8Φ = 1007+50 = 1057 mm
For 20Φ bars 806 + 2Φ = 806+40 = 846 mm
(v) Design for Shear
Tensile steel provided at Left End = 2116
Permissible Design Stress of Concrete
(As per Table ndash 19 of IS 4562000) τc = 0835 MPa
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Design Shear Strength of Concrete = τc b d
= (0835 X 250 X 490) 1000
= 102 KN
Similarly Design Shear Strength of Concrete at centre for Ast = 0512
τc = 0493 MPa
Shear Strength of Concrete at centre = τc b d
= (0493 X 250 X 490) 1000
= 6040 KN
(vi) Shear force due to Plastic Hinge Formation at the ends of the beam
The additional shear due to formation of plastic hinges at both ends of the beams is evaluated
as per Cl 633 of IS 139201993 is given by
Vsway to right = plusmn 14 [MulimAs
+ MulimBh
] L
Vsway to left = plusmn 14 [MulimAh
+ MulimBs
] L
Where
MulimAs
= Sagging Ultimate Moment of Resistance of Beam Section at End A
MulimAh
= Hogging Ultimate Moment of Resistance of Beam Section at End A
MulimBh
= Sagging Ultimate Moment of Resistance of Beam Section at End B
MulimBs
= Hogging Ultimate Moment of Resistance of Beam Section at End B
At Ends beam is provided with steel ndash pt = 2116 pc = 1058
Referring Table 51 of SP ndash 16 for pt = 2116 pc = 1058
The lowest value of MuAh
bd2 is found
MuAh
bd2 = 645
Hogging Moment Capacity at End A
MuAh
= 645 X 250 X 4902
= 38716 X 108 N-mm
= 38716 KN-m
Similarly for MuAs
pt = 1058 pc = 2116
Contribution of Compressive steel is ignored while calculating the Sagging Moment
Capacity at T-beam
MuAs
= 087 fy Ast d [1- (Ast fy bf d fck)]
= 087 X 415 X 1658 X 490 [1ndash (1658 X 415 1617 X 490 X 25)]
= 28313 KN-m
Similarly for Right End of beam
MuBh
= 38716 KN-m amp MuBs
= 28313 KN-m
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Shear due to Plastic Hinge is calculated as
Vsway to right = plusmn 14 [MuAs
+ MuBh
] L
= plusmn 14 [28313 + 38716] 4
= 23460 KN
Vsway to left = plusmn 14 [MuAh
+ MuBs
] L
= plusmn 14 [38716 + 28313] 4
= 23460 KN
Design Shear
Dead Load of Slab = 50 KNm2 Live Load = 40 KNm
2
Load due to Slab in Beam AB = 2 X [12 X 4 X 2] X 5 = 40 KN (10 KNm)
Self Wt Of Beam = 025 X 055 X 25 X 4 = 1375 KN (344 KNm)
asymp 1400 KN
Live Load = 2 X [12 X 4 X 2] X 4 = 32 KN (8 KNm)
Shear Force due to DL = 12 X [40 + 14] = 27 KN
Shear Force due to LL = 12 X [32] = 16 KN
As per Cl 633 of IS 139201993 the Design shear at End A ie Vua and Design Shear at
End B ie Vub are computed as
(i) For Sway Right
Vua = VaD+L
ndash 14 [MulimAs
+ MulimBh
] LAB
Vub = VbD+L
+ 14 [MulimAs
+ MulimBh
] LAB
(ii) For Sway Left
Vua = VaD+L
+ 14 [MulimAh
+ MulimBs
] LAB
Vub = VbD+L
ndash 14 [MulimAh
+ MulimBs
] LAB
Where
VaD+L
amp VbD+L
= Shear at ends A amp B respectively due to vertical load with
Partial Safety Factor of 12 on Loads
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VaD+L
= VbD+L
= 12 (D+L) 2
--------------For equ (i)
---------------For equ (ii)
14 X [MuAs
+ MuBh
] L = 23460 KN
14 X [MuAh
+ MuBs
] L = 23460 KN
VaD = Vb
D = 12 X 27 = 324
= 516
VaL = Vb
L = 12 X 16 = 192
Vua = [12 (27+16)] ndash 23460 = 516 ndash 23460 = (-) 18300 KN
Vub = [12 (27+16)] + 23460 = 516 + 23460 = (+) 28620 KN
Vub = [12 (27+16)] + 23460 = 516 + 23460 = (+) 28620 KN
Vua = [12 (27+16)] ndash 23460 = 516 ndash 23460 = (-) 18300 KN
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As per Cl 633 of IS 139201993 the Design Shear Force to be resisted shall be of
maximum of
(i) Calculate factored SF as per analysis ( Refer Table ndash B)
(ii) Shear Force due to formation of Plastic Hinges at both ends of the beam plus
factored gravity load on the span
Hence Design shear Force Vu will be 28620 KN (corresponding to formation of Plastic
Hinge)
From Analysis as per Table ndash B SF at mid-span of the beam is 127 KN However Shear
due to formation of Plastic Hinge is 23460 KN Hence design shear at centre of span is
taken as 23460 KN
The required capacity of shear reinforcement at ends
Vus = Vu - Vc
= 28620 ndash 102
= 18420 KN
And at centre Vus = 23460 ndash 6040
= 17420 KN
At supports
Vus d = 28620 49 = 584 KNcm
Therefore requirement of stirrups is
12Φ ndash 2 legged strippus 135 cc [Vus d = 606]
However provide 12Φ ndash 2 legged strippus 120 cc as per provision of Cl 635 of IS
139201993 [Vus d = 6806]
At centre
Vus d = 23460 49 = 478 KNcm
Provide 12Φ ndash 2 legged strippus 170 cc [Vus d = 4804]
As per Cl 635 of IS 139201993 the spacing of stirrups in the mid-span should not
exceed d2 = 4902 = 245 mm
Minimum Shear Reinforcement as per Cl 26516 of IS 4562000 is
Sv = Asv X 08 fy 046
= (2 X 79 X 087 X 415) (250 X 04)
= 570 mm
As per CL 635 of IS 139201993 ldquoSpacing of Links over a length of 2d at either end of
beam shall not exceed
(i) d4 = 4904 = 12250 mm
(ii) 8 times dia of smallest longitudinal bar = 8 X 16 = 128 mm
However it need not be less than 100 mm
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The reinforcement detailing is shown as below
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अधयाय Chapter ndash 10
अलप सामरथय तचनाई सोरचनाओो क तनमायण Construction of Low Strength Masonry Structures
Two types of construction are included herein namely
a) Brick construction using weak mortar and
b) Random rubble and half-dressed stone masonry construction using different mortars such as
clay mud lime-sand and cement sand
101 भको प क दौरान ईोट तचनाई की दीवारो ो का वयविार Behaviour of Brick Masonry Walls
during Earthquakes
Of the three components of a masonry building (roof wall and foundation as illustrated in
Fig101) the walls are most vulnerable to damage caused by horizontal forces due to earthquake
Ground vibrations during earthquakes cause inertia forces at locations of mass in the building (Fig 102) These forces travel through the roof and walls to the foundation The main emphasis
is on ensuring that these forces reach the ground without causing major damage or collapse
A wall topples down easily if pushed
horizontally at the top in a direction
perpendicular to its plane (termed weak
Fig 101 Basic components of Masonry Building
Fig 103 For the direction of Earthquake shaking
shown wall B tends to fail
at its base
Fig 102 Effect of Inertia in a building when shaken
at its base
Fig 104 Direction of force on a wall critically determines
its earthquake performance
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direction) but offers much greater resistance if pushed along its length (termed strong direction) (Fig 103 amp 104)
The ground shakes simultaneously in the vertical and two horizontal directions during
earthquakes However the horizontal vibrations are the most damaging to normal masonry
buildings Horizontal inertia force developed at the
roof transfers to the walls acting either in the weak
or in the strong direction If all the walls are not tied
together like a box the walls loaded in their weak
direction tend to topple
To ensure good seismic performance all walls must
be joined properly to the adjacent walls In this way
walls loaded in their weak direction can take
advantage of the good lateral resistance offered by
walls loaded in their strong direction (Fig 105)
Further walls also need to be tied to the roof and
foundation to preserve their overall integrity
102 तचनाई वाली इमारिो ो म बॉकस एकशन कस सतनतिि कर How to ensure Box Action in
Masonry Buildings
A simple way of making these walls behave well during earthquake shaking is by making them
act together as a box along with the roof at the top and with the foundation at the bottom A
number of construction aspects are required to ensure this box action
Firstly connections between the walls should be good This can be achieved by (a) ensuring
good interlocking of the masonry courses at the junctions and (b) employing horizontal bands
at various levels particularly at the lintel level
Secondly the sizes of door and window
openings need to be kept small The smaller
the opening the larger is the resistance
offered by the wall
Thirdly the tendency of a wall to topple
when pushed in the weak direction can be
reduced by limiting its length-to-thickness
and height to-thickness ratios Design codes
specify limits for these ratios A wall that is
too tall or too long in comparison to its
thickness is particularly vulnerable to
shaking in its weak direction (Fig 106)
Fig 106 Slender walls are vulnerable
Fig 105 Wall B properly connected to Wall A
(Note roof is not shown) Walls A
(loaded in strong direction) support
Walls B (loaded in weak direction)
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Brick masonry buildings have large mass and hence attract large horizontal forces during
earthquake shaking They develop numerous cracks under both compressive and tensile forces
caused by earthquake shaking The focus of earthquake resistant masonry building construction
is to ensure that these effects are sustained without major damage or collapse Appropriate choice
of structural configuration can help achieve this
The structural configuration of masonry buildings
includes aspects like (a) overall shape and size of the
building and (b) distribution of mass and
(horizontal) lateral load resisting elements across the
building
Large tall long and un-symmetric buildings perform
poorly during earthquakes A strategy used in making
them earthquake resistant is developing good box
action between all the elements of the building ie
between roof walls and foundation (Fig 107) For
example a horizontal band introduced at the lintel
level ties the walls together and helps to make them
behave as a single unit
103 कषतिज बि की भतमका Role of Horizontal Bands
Horizontal bands are the most important
earthquake-resistant feature in masonry
buildings The bands are provided to hold a
masonry building as a single unit by tying all
the walls together and are similar to a closed
belt provided around cardboard boxes
(Fig 108 amp 109)
The lintel band undergoes bending and pulling actions during earthquake shaking
(Fig1010)
To resist these actions the construction of lintel band requires special attention
Fig 107 Essential requirements to ensure
box action in a masonry building
Fig 108 Building with flat roof
Fig 109 Two-storey Building with pitched roof
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Bands can be made of wood (including bamboo splits) or of reinforced concrete (RC) the
RC bands are the best (Fig 1011)
The straight lengths of the band must be properly connected at the wall corners
In wooden bands proper nailing of straight lengths with spacers is important
In RC bands adequate anchoring of steel links with steel bars is necessary
The lintel band is the most important of all and needs to be provided in almost all buildings
The gable band is employed only in buildings with pitched or sloped roofs
In buildings with flat reinforced concrete or reinforced brick roofs the roof band is not
required because the roof slab also plays the role of a band However in buildings with flat
timber or CGI sheet roof roof band needs to be provided In buildings with pitched or sloped
roof the roof band is very important
Plinth bands are primarily used when there is concern about uneven settlement of foundation
soil
Lintel band Lintel band is a band provided at lintel level on all load bearing internal external
longitudinal and cross walls
Roof band Roof band is a band provided immediately below the roof or floors Such a band
need not be provided underneath reinforced concrete or brick-work slabs resting on bearing
Fig 1010 Bending and pulling in lintel bands ndash Bands must be capable of resisting these actions
Fig 1011 Horizontal Bands in masonry buildings ndash RC bands are the best
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walls provided that the slabs are continuous over the intermediate wall up to the crumple
sections if any and cover the width of end walls fully or at least 34 of the wall thickness
Gable band Gable band is a band provided at the top of gable masonry below the purlins This
band shall be made continuous with the roof band at the eaves level
Plinth band Plinth band is a band provided at plinth level of walls on top of the foundation
wall This is to be provided where strip footings of masonry (other than reinforced concrete or
reinforced masonry) are used and the soil is either soft or uneven in its properties as frequently
happens in hill tracts This band will serve as damp proof course as well
104 अधोलोब सदढीकरण Vertical Reinforcement
Vertical steel at corners and junctions of walls which are up to 340 mm (1frac12 brick) thick shall be
provided as specified in Table 101 For walls thicker than 340 mm the area of the bars shall be
proportionately increased
No vertical steel need be provided in category A building The vertical reinforcement shall be
properly embedded in the plinth masonry of foundations and roof slab or roof band so as to
develop its tensile strength in bond It shall be passing through the lintel bands and floor slabs or
floor level bands in all storeys
Table ndash 101 Vertical Steel Reinforcement in Masonry Walls with Rectangular Masonry Units (IS 4326 1993)
No of Storeys Storey Diameter of HSD Single Bar in mm at Each Critical Section
Category B Category C Category D Category E One mdash Nil Nil 10 12
Two Top
Bottom
Nil
Nil
Nil
Nil
10
12
12
16
Three Top
Middle
Bottom
Nil
Nil
Nil
10
10
12
10
12
12
12
16
16
Four Top
Third
Second
Bottom
10
10
10
12
10
10
12
12
10
12
16
20
Four storeyed
building not
permitted
NOTES
1 The diameters given above are for HSD bars For mild-steel plain bars use equivalent diameters as given under
Table ndash 106 Note 2
2 The vertical bars will be covered with concrete M15 or mortar 1 3 grade in suitably created pockets around the
bars This will ensure their safety from corrosion and good bond with masonry
3 In case of floorsroofs with small precast components also refer 923 of IS 4326 1993 for floorroof band details
Bars in different storeys may be welded (IS 2751 1979 and IS 9417 1989 as relevant) or
suitably lapped
Vertical reinforcement at jambs of window and door openings shall be provided as per
Table ndash 101 It may start from foundation of floor and terminate in lintel band (Fig 1017)
Typical details of providing vertical steel in brickwork masonry with rectangular solid units
at corners and T-junctions are shown in Fig 1012
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105 दीवारो ो म सराखो ो का सोरकषण Protection of Openings in Walls
Horizontal bands including plinth band lintel band and roof band are provided in masonry
buildings to improve their earthquake performance Even if horizontal bands are provided
masonry buildings are weakened by the openings in their walls
Embedding vertical reinforcement bars in the edges of the wall piers and anchoring them in the
foundation at the bottom and in the roof band at the top forces the slender masonry piers to
undergo bending instead of rocking In wider wall piers the vertical bars enhance their capability
to resist horizontal earthquake forces and delay the X-cracking Adequate cross-sectional area of
these vertical bars prevents the bar from yielding in tension Further the vertical bars also help
protect the wall from sliding as well as from collapsing in the weak direction
However the most common damage observed after an earthquake is diagonal X-cracking of
wall piers and also inclined cracks at the corners of door and window openings
When a wall with an opening deforms during earthquake shaking the shape of the opening
distorts and becomes more like a rhombus - two opposite corners move away and the other two
come closer Under this type of deformation the corners that come closer develop cracks The
cracks are bigger when the opening sizes are larger Steel bars provided in the wall masonry all
Fig 1012 Typical Details of Providing Vertical Steel Bars in Brick Masonry (IS 4326 1993)
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around the openings restrict these cracks at the corners In summary lintel and sill bands above
and below openings and vertical reinforcement adjacent to vertical edges provide protection
against this type of damage (Fig 1013)
106 भको प परतिरोधी ईोट तचनाई भवन क तनमायण िि सामानय तसदाोि General Principles for
Construction of Earthquake Resistant Brick Masonry Building
Low Strength Masonry constructions should not be permitted for important buildings
It will be useful to provide damp-proof course at plinth level to stop the rise of pore water
into the superstructure
Precautions should be taken to keep the rain water away from soaking into the wall so that
the mortar is not softened due to wetness An effective way is to take out roof projections
beyond the walls by about 500 mm
Use of a water-proof plaster on outside face of walls will enhance the life of the building and
maintain its strength at the time of earthquake as well
Ignoring tensile strength free standing walls should be checked against overturning under the
action of design seismic coefficient ah allowing for a factor of safety of 15
1061 भवनो ो की शरतणयाा Categories of Buildings
For the purpose of specifying the earthquake resistant features in masonry and wooden buildings
the buildings have been categorized in five categories A to E based on the seismic zone and the
importance of building I
Where
I = importance factor applicable to the
building [Ref Clause 642 and
Table - 6 of IS 1893 (Part 1) 2002]
The building categories are given in
Table ndash 102
Fig 1013 Cracks at corners of openings in a masonry building ndash reinforcement around them helps
Table -102 Building Categories for Earthquake Resisting Features (IS 4326 1993)
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1062 कमजोर गार म ईोट तचनाई कायय Brickwork in Weak Mortars
The fired bricks should have a compressive strength not less than 35 MPa Strength of bricks
and wall thickness should he selected for the total building height
The mortar should be lime-sand (13) or clay mud of good quality Where horizontal steel is
used between courses cement-sand mortar (13) should be used with thickness so as to cover
the steel with 6 mm mortar above and below it Where vertical steel is used the surrounding
brickwork of 1 X 1 or lfrac12 X 1frac12 brick size depending on wall thickness should preferably be
built using 16 cement-sand mortar
The minimum wall thickness shall be one brick in one storey construction and one brick in
top storey and 1frac12brick in bottom storeys of up to three storey constructions It should also
not be less than l16 of the length of wall between two consecutive perpendicular walls
The height of the building shall be restricted to the following where each storey height shall
not exceed 30 m
For Categories A B and C - three storeys with flat roof and two storeys plus attic pitched
roof
For Category D - two storeys with flat roof and one storey plus attic for pitched roof
1063 आयिाकार तचनाई इकाइयो ो वाला तचनाई तनमायण Masonry Construction with
Rectangular Masonry Units
General requirements for construction of masonry walls using rectangular masonry units are
10631 तचनाई इकाइयाो Masonry Units
Well burnt bricks conforming to IS 1077 1992 or solid concrete blocks conforming to IS
2185 (Part 1) 1979 and having a crushing strength not less than 35 MPa shall be used The
strength of masonry unit required
shall depend on the number of storeys
and thickness of walls
Squared stone masonry stone block
masonry or hollow concrete block
masonry as specified in IS 1597 (Part
2) 1992 of adequate strength may
also be used
10632 गारा Mortar
Mortars such as those given in Table
ndash 103 or of equivalent specification
shall preferably be used for masonry
Table ndash 103 Recommended Mortar Mixes (IS 4326 1993)
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construction for various categories of buildings
Where steel reinforcing bars are provided in masonry the bars shall be embedded with
adequate cover in cement sand mortar not leaner than 13 (minimum clear cover 10 mm) or in
cement concrete of grade M15 (minimum clear cover 15 mm or bar diameter whichever
more) so as to achieve good bond and corrosion resistance
1064 दीवार Walls
Masonry bearing walls built in mortar as specified in 10632 above unless rationally
designed as reinforced masonry shall not be built of greater height than 15 m subject to a
maximum of four storeys when measured from the mean ground level to the roof slab or
ridge level
The bearing walls in both directions shall be straight and symmetrical in plan as far as
possible
The wall panels formed between cross walls and floors or roof shall be checked for their
strength in bending as a plate or as a vertical strip subjected to the earthquake force acting on
its own mass
Note mdash For panel walls of 200 mm or larger thickness having a storey height not more than
35 metres and laterally supported at the top this check need not be exercised
1065 तचनाई बॉणड Masonry Bond
For achieving full strength of
masonry the usual bonds
specified for masonry should be
followed so that the vertical joints
are broken properly from course
to course To obtain full bond
between perpendicular walls it is
necessary to make a slopping
(stepped) joint by making the
corners first to a height of 600
mm and then building the wall in
between them Otherwise the
toothed joint (as shown in Fig
1014) should be made in both the
walls alternatively in lifts of
about 450 mm
Panel or filler walls in framed buildings shall be properly bonded to surrounding framing
members by means of suitable mortar (as given in 10632 above) or connected through
dowels
Fig 1014 Alternating Toothed Joints in Walls at Corner and T-Junction (IS 4326 1993)
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107 ओपतनोग का परभाव Influence of Openings
Openings are functional necessities in buildings
During earthquake shaking inertia forces act in
the strong direction of some walls and in the weak
direction of others Walls shaken in the weak
direction seek support from the other walls ie
walls B1 and B2 seek support from walls A1 and
A2 for shaking in the direction To be more
specific wall B1 pulls walls A1 and A2 while
wall B2 pushes against them
Thus walls transfer loads to each other at their
junctions (and through the lintel bands and roof)
Hence the masonry courses from the walls
meeting at corners must have good interlocking
(Fig 1015) For this reason openings near the
wall corners are detrimental to good seismic
performance Openings too close to wall corners
hamper the flow of forces from one wall to
another Further large openings weaken walls
from carrying the inertia forces in their own
plane Thus it is best to keep all openings as small as possible and as far away from the corners
as possible
108 धारक दीवारो ो म ओपतनोग परदाि करि की सामानय आवशयकताए General Requirements of
Providing Openings in Bearing Walls
Door and window openings in walls reduce their lateral load resistance and hence should
preferably be small and more centrally located The guidelines on the size and position of
opening are given in Table ndash 104 and in Fig 1016
Fig 1015 Regions of force transfer from weak
walls to strong walls in a masonry building ndash Wall
B1 pulls walls A1 and A2 while wall B2pushes walls
A1 and A2
Fig 1016 Dimensions of Openings and Piers for
Recommendations in Table 3 (IS 4326 1993)
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101
Table ndash 104 Size and Position of Openings in Bearing Walls
S
No
Position of opening Details of Opening for Building Category
A and B C D and E
1 Distance b5 from the inside corner of outside wall Min Zero mm 230 mm 450 mm
2 For total length of openings the ratio (b1+b2+b3)l1 or
(b6+b7)l2 shall not exceed
a) one-storeyed building
b) two-storeyed building
c) 3 or 4-storeyed building
060
050
042
055
046
037
050
042
033
3 Pier width between consecutive openings b4 Min 340 mm 450 mm 560 mm
4 Vertical distance between two openings one above the
other h3 Min
600 mm 600 mm 600 mm
5 Width of opening of ventilator b8 Max 900 mm 900 mm 900 mm
Openings in any storey shall preferably have their top at the same level so that a continuous
band could be provided over them including the lintels throughout the building
Where openings do not comply with the guidelines as given in Table ndash 104 they should be
strengthened by providing reinforced concrete or reinforcing the brickwork as shown in Fig
1017 with high strength deformed (HSD) bars of 8 mm dia but the quantity of steel shall be
increased at the jambs
If a window or ventilator is to be
projected out the projection shall be in
reinforced masonry or concrete and well
anchored
If an opening is tall from bottom to
almost top of a storey thus dividing the
wall into two portions these portions
shall be reinforced with horizontal
reinforcement of 6 mm diameter bars at
not more than 450 mm intervals one on
inner and one on outer face properly tied
to vertical steel at jambs corners or
junction of walls where used
The use of arches to span over the
openings is a source of weakness and
shall be avoided Otherwise steel ties
should be provided
109 भको पी सदढ़ीकरण वयवसथा Seismic Strengthening Arrangements
All masonry buildings shall be strengthened as specified for various categories of buildings as
listed in Table ndash 105
Fig 1017 Strengthening Masonry around Opening (IS
4326 1993)
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102
Table ndash 105 Strengthening Arrangements Recommended for Masonry Buildings
(Rectangular Masonry Units)(IS 4326 1993)
Building Category Number of Storeyes Strengthening to be Provided in all Storeys
A
i) 1 to 3
ii) 4
a
a b c
B
i) 1 to 3
ii) 4
a b c f g
a b c d f g
C
i) 1 and 2
ii) 3 and 4
a b c f g
a to g
D
i) 1 and 2
ii) 3 and 4
a to g
a to h
E 1 to 3 a to h
Where
a mdash Masonry mortar
b mdash Lintel band
c mdash Roof band and gable band where necessary
d mdash Vertical steel at corners and junctions of walls
e mdash Vertical steel at jambs of openings
f mdash Bracing in plan at tie level of roofs
g mdash Plinth band where necessary and
h mdash Dowel bars
4th storey not allowed in category E
NOTE mdash In case of four storey buildings of category B the requirements of vertical steel may be checked
through a seismic analysis using a design seismic coefficient equal to four times the one given in (a) 3423
of IS 1893 1984 (This is because the brittle behaviour of masonry in the absence of vertical steel results in
much higher effective seismic force than that envisaged in the seismic coefficient provided in the code) If
this analysis shows that vertical steel is not required the designer may take the decision accordingly
The overall strengthening arrangements to be adopted for category D and E buildings which
consist of horizontal bands of reinforcement at critical levels vertical reinforcing bars at corners
junctions of walls and jambs of opening are shown in Fig 1018 amp 1019
Fig 1018 Overall Arrangement of Reinforcing Fig 1019 Overall Arrangement of Reinforcing Masonry
Masonry Buildings (IS 4326 1993) Building having Pitched Roof (IS 4326 1993)
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103
1091 पटट का अनभाग एवो सदढीकरण Section and Reinforcement of Band
The band shall be made of reinforced concrete of grade not leaner than M15 or reinforced
brickwork in cement mortar not leaner than 13 The bands shall be of the full width of the wall
not less than 75 mm in depth and reinforced with steel as indicated in Table ndash 106
Table ndash 106 Recommended Longitudinal Steel in Reinforced Concrete Bands (IS 4326 1993)
Span Building Category
B
Building Category
C
Building Category
D
Building Category
E No of Bars Dia No of Bars Dia No of Bars Dia No of Bars Dia
(1) (2) (3) (4) (5) (6) (7) (8) (9)
m mm mm mm mm
5 or less 2 8 2 8 2 8 2 10
6 2 8 2 8 2 10 2 12
7 2 8 2 10 2 12 4 10
8 2 10 2 12 4 10 4 12
Notes -
1 Span of wall will be the distance between centre lines of its cross walls or buttresses For spans greater than 8 m
it will be desirable to insert pillasters or buttresses to reduce the span or special calculations shall be made to
determine the strength of wall and section of band
2 The number and diameter of bars given above pertain to high strength deformed bars If plain mild-steel bars are
used keeping the same number the following diameters may be used
High Strength Def Bar dia 8 10 12 16 20
Mild Steel Plain bar dia 10 12 16 20 25
3 Width of RC band is assumed same as the thickness of the wall Wall thickness shall be 200 mm minimum A
clear cover of 20 mm from face of wall will be maintained
4 The vertical thickness of RC band be kept 75 mm minimum where two longitudinal bars are specified one on
each face and 150 mm where four bars are specified
5 Concrete mix shall be of grade M15 of IS 456 1978 or 1 2 4 by volume
6 The longitudinal steel bars shall be held in position by steel links or stirrups 6 mm dia spaced at 150 mm apart
NOTE mdash In coastal areas the concrete grade shall be M20 concrete and the filling mortar of 13
(cement-sand with water proofing admixture)
As illustrated in Fig 1020 ndash
In case of reinforced brickwork the
thickness of joints containing steel bars shall
be increased so as to have a minimum
mortar cover of 10 mm around the bar In
bands of reinforced brickwork the area of
steel provided should be equal to that
specified above for reinforced concrete
bands
In category D and E buildings to further
iterate the box action of walls steel dowel
bars may be used at corners and T-junctions
of walls at the sill level of windows to
length of 900 mm from the inside corner in
each wall Such dowel may be in the form of
Fig 1020 Reinforcement and Bending Detail in RC Band ((IS 4326 1993)
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104
U stirrups 8 mm dia Where used such bars must be laid in 13 cement-sand-mortar with a
minimum cover of 10 mm on all sides to minimize corrosion
1010 भको प क दौरान सटोन तचनाई की दीवारो ो का वयविार Behaviour of Stone Masonry
Walls during Earthquakes
Stone has been used in building construction in India since ancient times since it is durable and
locally available The buildings made of thick stone masonry walls (thickness ranges from 600 to
1200 mm) are one of the most deficient building systems from earthquake-resistance point of
view
The main deficiencies include excessive wall thickness absence of any connection between the
two wythes of the wall and use of round stones (instead of shaped ones) (Fig 1021 amp 1022)
Note A wythe is a continuous vertical section of masonry one unit in thickness A wythe may be
independent of or interlocked with the adjoining wythe (s) A single wythe of brick that is not
structural in nature is referred to as a veneer (httpsenwikipediaorgwikiWythe)
The main patterns of earthquake damage include
(a) bulging separation of walls in the horizontal direction into two distinct wythes
(b) separation of walls at corners and T-junctions
(c) separation of poorly constructed roof from walls and eventual collapse of roof and
(d) disintegration of walls and eventual collapse of the whole dwelling
In the 1993 Killari (Maharashtra) earthquake alone over 8000 people died most of them buried
under the rubble of traditional stone masonry dwellings Likewise a majority of the over 13800
deaths during 2001 Bhuj (Gujarat) earthquake is attributed to the collapse of this type of
construction
1011 भको प परतिरोधी सटोन तचनाई भवन क तनमायण िि सामानय तसदाोि General principle for
construction of Earthquake Resistant stone masonry building
10111 भको प परतिरोधी लकषण Earthquake Resistant Features
1 Low strength stone masonry buildings are weak against earthquakes and should be avoided
in high seismic zones Inclusion of special earthquake-resistant features may enhance the
earthquake resistance of these buildings and reduce the loss of life These features include
Fig 1021 Separation of a thick wall into two layers Fig 1022 Separation of unconnected adjacent walls at junction
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105
(a) Ensure proper wall construction
(b) Ensure proper bond in masonry courses
(c) Provide horizontal reinforcing elements
(d) Control on overall dimensions and heights
2 The mortar should be cement-sand (1 6) lime-sand (1 3) or clay mud of good quality
3 The wall thickness should not be larger than 450
mm Preferably it should be about 350 mm and
the stones on the inner and outer wythes should be
interlocked with each other
NOTE - If the two wythes are not interlocked they
tend to delaminate during ground shaking bulge
apart (as shown in Fig 1023) and buckle
separately under vertical load leading to
complete collapse of the wall and the building
4 The masonry should preferably be brought to courses at not more than 600 mm lift
5 lsquoThroughrsquo stones at full length
equal to wall thickness should be
used in every 600 mm lift at not
more than 12 m apart
horizontally If full length stones
are not available stones in pairs
each of about 34 of the wall
thickness may be used in place of
one full length stone so as to
provide an overlap between them
(as shown in Fig 1024)
6 In place of lsquothroughrsquo stones lsquobonding elementsrsquo of steel bars 8 to 10 mm dia bent to S-shape
or as hooked links may be used with a cover of 25 mm from each face of the wall (as shown
in Fig 1024) Alternatively wood-bars of 38 mm X 38 mm cross section or concrete bars of
50 mm X50 mm section with an 8 mm dia rod placed centrally may be used in place of
throughrsquo stones The wood should be well treated with preservative so that it is durable
against weathering and insect action
7 Use of lsquobondingrsquo elements of adequate length should also be made at corners and junctions of
walls to break the vertical joints and provide bonding between perpendicular walls
8 Height of the stone masonry walls (random rubble or half-dressed) should be restricted as
follows with storey height to be kept 30 m maximum and span of walls between cross walls
to be limited to 50 m
Fig 1023 Wall delaminated with buckled
withes (IS 13828 1993)
Fig 1024 Through Stone and Bond Elements (IS 13828 1993)
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a) For categories A and B ndash Two storeys with flat roof or one storey plus attic if walls are
built in lime-sand or mud mortar and -one storey higher if walls are built in cement-sand
1 6 mortar
b) For categories C and D - Two storeys with flat roof or two storeys plus attic for pitched
roof if walls are built in 1 6 cement mortar and one storey with flat roof or one storey
plus attic if walls are built in lime-sand or mud mortar respectively
9 If walls longer than 5 m are needed buttresses may be used at intermediate points not farther
apart than 40 m The size of the buttress be kept of uniform thickness Top width should be
equal to the thickness of main wall t and the base width equal to one sixth of wall height
10 The stone masonry dwellings must have horizontal bands (plinth lintel roof and gable
bands) These bands can be constructed out of wood or reinforced concrete and chosen based
on economy It is important to provide at least one band (either lintel band or roof band) in
stone masonry construction
Note Although this type of stone masonry construction practice is deficient with regards to earthquake
resistance its extensive use is likely to continue due to tradition and low cost But to protect human lives
and property in future earthquakes it is necessary to follow proper stone masonry construction in seismic
zones III and higher Also the use of seismic bands is highly recommended
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107
अधयाय Chapter- 11
भकपीय रलयमकन और रटरोफिट ग
SEISMIC EVALUATION AND RETROFITTING
There are considerable number of buildings that do not meet the requirements of current design
standards because of inadequate design or construction errors and need structural upgrading
specially to meet the seismic requirements
Retrofitting is the best solution to strengthen such buildings without replacing them
111 भकपीय रलयमकन SEISMIC EVALUATION
Seismic evaluation is to assess the seismic response of buildings which may be seismically
deficient or earthquake damaged for their future use The evaluation is also helpful in choosing
appropriate retrofitting techniques
The methods available for seismic evaluation of existing buildings can be broadly divided into
two categories
1 Qualitative methods 2 Analytical methods
1111 गणमतरक िरीक QUALITATIVE METHODS
The qualitative methods are based on the available background information of the structures
past performance of similar structures under severe earthquakes visual inspection report some
non-destructive test results etc
Method for Seismic evaluation
Qualitative methods Analytic methods
CapacityDemand
method
Push over
analysis
Inelastic time
history method
Condition
assessment
Visual
inspection
Non-destructive
testing
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The evaluation of any building is a difficult task which requires a wide knowledge about the
structures cause and nature of damage in structures and its components material strength etc
The proposed methodology is divided into three components
1 Condition assessment
It is based on
data collection or information gathering of structures from architectural and structural
drawings
performance characteristics of similar type of buildings in past earthquakes
rapid evaluation of strength drift materials structural components and structural details
2 Visual inspectionField evaluation It is based on observed distress and damage in
structures Visual inspection is more useful for damaged structures however it may also be
conducted for undamaged structures
3 Non-destructive evaluation It is generally carried out for quick estimation of materials
strength determination of the extent of determination and to establish causes remain out of
reach from visual inspection and determination of reinforcement and its location NDT may
also be used for preparation of drawing in case of non-availability
11111 Condition Assessment for Evaluation
The aim of condition assessment of the structure is the collection of information about the
structure and its past performance characteristics to similar type of structure during past
earthquakes and the qualitative evaluation of structure for decision-making purpose More
information can be included if necessary as per requirement
(i) Data collection information gathering
Collection of the data is an important portion for the seismic evaluation of any existing building
The information required for the evaluated building can be divided as follows
Building Data
Architectural structural and construction drawings
Vulnerability parameters number of stories year of construction and total floor area
Specification soil reports and design calculations
Seismicity of the site
Construction Data
Identifications of gravity load resisting system
Identifications of lateral load resisting system
Maintenance addition alteration or modifications in structures
Field surveys of the structurersquos existing condition
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Structural Data
Materials
Structural concept vertical and horizontal irregularities torsional eccentricity pounding
short column and others
Detailing concept ductile detailing special confinement reinforcement
Foundations
Non-structural elements
(ii) Past Performance data
Past performance of similar type of structure during the earthquake provides considerable amount
of information for the building which is under evaluation process Following are the areas of
concerns which are responsible for poor performance of buildings during earthquake
Material concerns
Low grade on concrete
Deterioration in concrete and reinforcement
High cement-sand ratio
Corrosion in reinforcement
Use of recycled steel as reinforcement
Spalling of concrete by the corrosion of embedded reinforcing bars
Corrosion related to insufficient concrete cover
Poor concrete placement and porous concrete
Structural concerns
The relatively low stiffness of the frames excessive inter-storey drifts damage to non-
structural items
Pounding column distress possibly local collapse
Unsymmetrical buildings (U T L V) in plan torsional effects and concentration of damage
at the junctures (ie re-entrant corners)
Unsymmetrical buildings in elevation abrupt change in lateral resistance
Vertical strength discontinuities concentrate damage in the ldquosoftrdquo stories
Short column
Detailing concerns
Large tie spacing in columns lack of confinement of concrete core shear failures
Insufficient column lengths concrete to spall
Locations of inadequate splices brittle shear failure
Insufficient column strength for full moment hinge capacity brittle shear failure
Lack of continuous beam reinforcement hinge formation during load reversals
Inadequate reinforcing of beam column joints or location of beam bar splices at columns
joint failures
Improper bent-up of longitudinal reinforcing in beams as shear reinforcement shear failure
during load reversal
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110
Foundation dowels that are insufficient to develop the capacity of the column steel above
local column distress
(iii) Seismic Evaluation Data
Seismic evaluation of data will provide a general idea about the building performance during an
earthquake The criteria of evaluation of building will depend on materials strength and ductility
of structural components and detailing of reinforcement
Material Evaluation
Buildings height gt 3 stories minimum grade concrete M 20 desirable M 30 to M 40
particularly in columns of lower stories
Maximum grade of steel should be Fe 415 due to adequate ductility
No significant deterioration in reinforcement
No evidence of corrosion or spalling of concrete
Structural components
Evaluation of columns shear strength and drift check for permissible limits
Evaluation of plan irregularities check for torsional forces and concentration of forces
Evaluation of vertical irregularities check for soft storey mass or geometric discontinuities
Evaluation of beam-column joints check for strong column-weak beams
Evaluation of pounding check for drift control or building separation
Evaluation of interaction between frame and infill check for force distribution in frames and
overstressing of frames
(i) Flexural members
Limitation of sectional dimensions
Limitation on minimum and maximum flexural reinforcement at least two continuous
reinforced bars at top and bottom of the members
Restriction of lap splices
Development length requirements for longitudinal bars
Shear reinforcement requirements stirrup and tie hooks tie spacing bar splices
(ii) Columns
Limitation of sectional dimensions
Longitudinal reinforcement requirement
Transverse reinforcement requirements stirrup and tie hooks column tie spacing
column bar splices
Special confining requirements
(iii) Foundation
Column steel doweled into the foundation
Non-structural components
Cornices parapet and appendages are anchored
Exterior cladding and veneer are well anchored
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11112 Field Evaluation Visual Inspection Method
The procedure for visual inspection method is as below
Equipments
Optical magnification allows a detailed view of local areas of distress
Stereomicroscope that allow a three dimensional view of the surface Investigator can
estimate the elevation difference in surface features by calibrating the focus adjustment
screw
Fibrescope and borescopes allow inspection of regions that are inaccessible to the naked eye
Tape to measure the dimension of structure length of cracks
Flashlight to aid in lighting the area to be inspected particularly in post-earthquake
evaluation power failure
Crack comparator to measure the width of cracks at representative locations two types
plastic cards and magnifying lens comparators
Pencil to draw the sketch of cracks
Sketchpad to prepare a representation of wall elevation indicating the location of cracks
spalling or other damage records of significant features such as non-structural elements
Camera for photographs or video tape of the observed cracking
Action
Perform a walk through visual inspection to become familiar with the structure
Gather background documents and information on the design construction maintenance
and operation of structure
Plan the complete investigation
Perform a detailed visual inspection and observe type of damage cracks spalls and
delaminations permanent lateral displacement and buckling or fracture of reinforcement
estimating of drift
Observe damage documented on sketches interpreted to assess the behaviour during
earthquake
Perform any necessary sampling basis for further testing
Data Collection
To identify the location of vertical structural elements columns and walls
To sketch the elevation with sufficient details dimensions openings observed damage such
as cracks spalling and exposed reinforcing bars width of cracks
To take photographs of cracks use marker paint or chalk to highlight the fine cracks or
location of cracks in photographs
Observation of the non-structural elements inter-storey displacement
Limitations
Applicable for surface damage that can be visualised
No identification of inner damage health monitoring of building chang of frequency and
mode shapes
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11113 Non-destructive testing (NDT)
Visual inspection has the obvious limitation that only visible surface can be inspected Internal
defects go unnoticed and no quantitative information is obtained about the properties of the
concrete For these reasons a visual inspection is usually supplemented by NDT methods Other
detailed testing is then conducted to determine the extent and to establish causes
NDT tests for condition assessment of structures
Some methods of field and laboratory testing that may assess the minimum concrete strength and
condition and location of the reinforcement in order to characterize the strength safety and
integrity are
(i) Rebound hammer Swiss hammer
The rebound hammer is the most widely used non-destructive device for quick surveys to assess
the quality of concrete In 1948 Ernest Schmidt a Swiss engineer developed a device for testing
concrete based upon the rebound principal strength of in-place concrete comparison of concrete
strength in different locations and provides relative difference in strength only
Limitations
Not give a precise value of compressive strength provide estimate strength for comparison
Sensitive to the quality of concrete carbonation increases the rebound number
More reproducible results from formed surface rather than finished surface smooth hard-
towelled surface giving higher values than a rough-textured surface
Surface moisture and roughness also affect the reading a dry surface results in a higher
rebound number
Not take more than one reading at the same spot
(ii) Penetration resistance method ndash Windsor probe test
Penetration resistance methods are used to determine the quality and compressive strength of in-
situ concrete It is based on the determination of the depth of penetration of probes (steel rods or
pins) into concrete by means of power-actuated driver This provides a measure of the hardness
or penetration resistance of the material that can be related to its strength
Limitations
Both probe penetration and rebound hammer test provide means of estimating the relative
quality of concrete not absolute value of strength of concrete
Probe penetration results are more meaningful than the results of rebound hammer
Because of greater penetration in concrete the prove test results are influenced to a lesser
degree by surface moisture texture and carbonation effect
Probe test may be the cause of minor cracking in concrete
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(iii) Rebar locatorconvert meter
It is used to determine quantity location size and condition of reinforcing steel in concrete It is
also used for verifying the drawing and preparing as-built data if no previous information is
available These devices are based on interaction between the reinforcing bars and low frequency
electromagnetic fields Commercial convert meter can be divided into two classes those based
on the principal of magnetic reluctance and those based on eddy currents
Limitations
Difficult to interpret at heavy congestion of reinforcement or when depth of reinforcement is
too great
Embedded metals sometimes affect the reading
Used to detect the reinforcing bars closest to the face
(iv) Ultrasonic pulse velocity
It is used for determination the elastic constants (modulus of elasticity and Poissonrsquos ratio) and
the density By conducting tests at various points on a structure lower quality concrete can be
identified by its lower pulse velocity Pulse-velocity measurements can detect the presence of
voids of discontinuities within a wall however these measurements can not determine the depth
of voids
Limitations
Moisture content an increase in moisture content increases the pulse velocity
Presence of reinforcement oriented parallel to the pulse propagation direction the pulse may
propagate through the bars and result is an apparent pulse velocity that is higher than that
propagating through concrete
Presence of cracks and voids increases the length of the travel path and result in a longer
travel time
(v) Impact echo
Impact echo is a method for detecting discontinuities within the thickness of a wall An impact-
echo test system is composed of three components an impact source a receiving transducer and
a waveform analyzer or a portable computer with a data acquisition
Limitations
Accuracy of results highly dependent on the skill of the engineer and interpreting the results
The size type sensitivity and natural frequency of the transducer ability of FFT analyzer
also affect the results
Mainly used for concrete structures
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(vi) Spectral analysis of surface waves (SASW)
To assess the thickness and elastic stiffness of material size and location of discontinuities
within the wall such as voids large cracks and delimitations
Limitations
Interpretation of results is very complex
Mainly used on slab and other horizontal surface to determine the stiffness profiles of soil
sites and of flexible and rigid pavement systems measuring the changes in elastic properties
of concrete slab
(vii) Penetrating radar
It is used to detect the location of reinforcing bars cracks voids or other material discontinuities
verify thickness of concrete
Limitations
Mainly used for detecting subsurface condition of slab-on-grade
Not useful for detecting the small difference in materials
Not useful for detecting the size of bars closely spaced bars make difficult to detect features
below the layer of reinforcing steel
1112 ववशलषणमतरक िरीक ANALYTICAL METHODS
Analytical methods are based on considering capacity and ductility of the buildings which are
based on detailed dynamic analysis of buildings The methods in this category are
capacitydemand method pushover analysis inelastic time history analysis etc Brief discussions
on the method of evaluation are as follows
11121 CapacityDemand (CD) method
The forces and displacements resulting from an elastic analysis for design earthquake are
called demand
These are compared with the capacity of different members to resist these forces and
displacements
A (CD) ratio less than one indicate member failure and thus needs retrofitting
When the ductility is considered in the section the demand capacity ratio can be equated to
section ductility demand of 2 or 3
The main difficulty encountered in using this method is that there is no relationship between
member and structure ductility factor because of non-linear behaviour
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11122 Push Over Analysis
The push over analysis of a structure is a static non-linear analysis under permanent vertical
loads and gradually increasing lateral loads
The equivalent static lateral loads approximately represent earthquake-induced forces
A plot of total base shear verses top displacement in a structure is obtained by this analysis
that would indicate any premature failure or weakness
The analysis is carried out up to failure thus it enables determination of collapse load and
ductility capacity
On a building frame loaddisplacement is applied incrementally the formation of plastic
hinges stiffness degradation and plastic rotation is monitored and lateral inelastic force
versus displacement response for the complete structure is analytically computed
This type of analysis enables weakness in the structure to be identified The decision to
retrofit can be taken on the basis of such studies
11123 Inelastic time-history analysis
A seismically deficient building will be subjected to inelastic action during design earthquake
motion
The inelastic time history analysis of the building under strong ground motion brings out the
regions of weakness and ductility demand in the structure
This is the most rational method available for assessing building performance
There are computer programs available to perform this type of analysis
However there are complexities with regard to biaxial inelastic response of columns
modelling of joints behaviour interaction of flexural and shear strength and modelling of
degrading characteristics of member
The methodology is used to ascertain deficiency and post-elastic response under strong
ground shaking
Fig ndash 111 Strengthening strategies
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112 भवनो की रटरोफिट ग Retrofitting of Building
Retrofitting is to upgrade the strength and structural capacity of an existing structure to enable it
to safely withstand the effect of strong earthquakes in future
1121 सकटरचरल लवल यम गलोबल रटरोफि िरीक Structural Level or Global Retrofit
Methods
Two approaches are used for structural-level retrofitting
(i) Conventional Methods
(ii) Non-conventional methods
Retrofit procedure
Detailed seismic
evaluation
Retrofit
techniques
Seismic capacity
assessment
Selection of retrofit
scheme
Design of retrofit
scheme and detailing
Re-evaluation of
retrofit structure
Addition of infill walls
Addition of new
external walls
Addition of bracing
systems
Construction of wing
walls
Strengthening of
weak elements
Structural Level or Global Member Level or Local
Seismic Base Isolation
Jacketing of beams
Jacketing of columns
Jacketing of beam-
column joints
Strengthening of
individual footings
Seismic Dampers
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11211 Conventional Methods
Conventional Methods are based on increasing the seismic resistance of existing structure The
main categories of these methods are as follow
a) Addition of infilled walls
b) Addition of new external walls
c) Addition of bracing system
d) Construction of wing walls
e) Strengthening of weak elements
112111 Addition of infilled walls
The construction of infill walls within the frames of the load bearing structures as shown in the
example of Fig ndash 112 aims to drastically increase the strength and the stiffness of the structure
This method can also be applied in order to correct design errors in the structure and more
specifically when a large asymmetric distribution of strength or stiffness in elevation or an
eccentricity of stiffness in plan have been recognised
Fig - 112 Addition of infilled wall and wing walls
Fig - 113 Frames and shear wall
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As shown in Fig ndash 114 there are two alternatives methods of adding infill walls Either the infill
wall is simply placed between two existing columns or it is extended around the columns to form
a jacket The second method is specifically recommended in order to increase the strength in this
region In the situation where the existing columns are very weak a steel cage should be placed
around the columns before constructing new walls and column jackets In all cases the base of
any new wall should always be connected to the existing foundation
112112 Addition of new external walls
In some cases strengthening by adding concrete walls can be performed externally This can
often be carried out for functional reasons as for example in cases when the building must be
kept in operation during the intervention works New cast-in-place concrete walls constructed
outside the building can be designed to resist part or all the total seismic forces induced in the
building The new walls are preferably positioned adjacent to vertical elements (columns or
walls) of the building and are connected to the structure by placing special compression tensile
or shear connectors at every floor level of the building As shown in Figure 115 new walls
usually have a L-shaped cross-section and are constructed to be in contact with the external
corners of the building
Fig ndash 114 Two alternative methods of adding infill walls
Fig ndash 115 Schematic arrangement of connections between the existing building and
a new wall (a) plan (b) section of compression connector and (c) section of tension
connector
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It is important to ensure that connectors behave elastically under seismic design action effects
For this reason when designing the connectors a resistance safety factor equal to 14 is
recommended The use of compression and tensile connectors instead of shear connectors is
strongly recommended as much higher forces can be transferred It is essential that the anchorage
areas for the connectors on the existing
building and on the new walls have
enough strength to guarantee the transfer
of forces between new walls and the
existing structures
A very important issue of the above
method concerns the foundation of new
walls Foundation conditions should be
improved if large axial forces can be
induced in new walls during seismic
excitation In addition the construction
of short cantilever beams protruding from
the wall underneath the adjacent beams
at every floor level of the building as
shown in Fig ndash 116 appears to be a good solution
112113 Addition of bracing systems
The construction of bracing within
the frames of the load bearing
structure aims for a high increase
in the stiffness and a considerable
increase in the strength and
ductility of the structure Bracing
is normally constructed from steel
elements rather than reinforced
concrete as the elastic
deformation of steel aids the
absorption of seismic energy
Bracing systems can be used in a similar way as that for
steel constructions and can be applied easily in single-
storey industrial buildings with a soft storey ground floor
level where no or few brick masonry walls exist between
columns
Various truss configurations have been applied in
practice examples of which are K-shaped diamond
shaped or cross diagonal The latter is the most common
and is often the most effective solution
Fig ndash 116 Construction of cantilever beams to
transfer axial forces to new walls (a) plan (b)
section c-c
Fig ndash 117 Reinforced Concrete Building retrofitted
with steel bracing
Fig ndash 118 Steel bracing soft storey
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Use of steel bracing has a potential advantage over other schemes for the following reasons
Higher strength and stiffness can be proved
Opening for natural light can be
made easily
Amount of work is less since
foundation cost may be minimised
Bracing system adds much less
weight to the existing structure
Most of the retrofitting work can
be performed with prefabricated
elements and disturbance to the
occupants may be minimised
112114 Construction of wing wall
The construction of reinforced
concrete wing walls in continuous
connection with the existing columns
of a structure as shown above in
example of Fig ndash 112 is a very
popular technique
As presented in Fig ndash 1110 there are
two alternative methods of connecting
the wing wall to the existing load
bearing structure
In the first method the wall is connected to the column and the beams at the top and the base
of any floor level Steel dowels or special anchors are used for the connection and the
reinforcement of the new wall is welded to the existing reinforcement
In the second method the new wing wall is extended around the column to form a jacket
Obviously in this case stresses at the interface between the new concrete and the existing
column are considerably lower when compared to the first method
Moreover uncertainties regarding the capacity of the connection between the wall and the
column do not affect the seismic performance of the strengthened element Therefore the second
alternative method is strongly recommended
Fig ndash 1110 Construction of reinforced concrete wing
wall
Fig ndash 119 Steel bracing
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112115 Strengthening weak elements
The selective strengthening of weak elements of the
structure aims to avoid a premature failure of the critical
elements of a building and to increase the ductility of the
structure
Usually this method is applied to vertical elements and
is accompanied by the construction of fibre reinforced
polymer (FRP) jackets or as shown in Fig- 1111 steel
cages around the vertical elements
If a strength increase is also required this method can
include the construction of column jackets of shotcrete
or reinforced concrete
11212 Non-conventional methods
These are based on reduction of seismic demands Seismic demands are the force and
displacement resulting from an elastic analysis for earthquake design Incorporation of energy
absorbing systems to reduce seismic demands are as follows
(i) Seismic Base Isolation
(ii) Seismic Dampers
112121 Seismic Base Isolation
Isolation of
superstructure from the
foundation is known as
base isolation
It is the most powerful
tool for passive
structural vibration
control technique
Types of base isolations
Elastomeric Bearings
This is the most widely used Base Isolator
The elastomer is made of either Natural Rubber or Neoprene
The structure is decoupled from the horizontal components of the earthquake ground motion
Fig ndash 1111 Construction of a steel
cage around a vertical element
Fig ndash 1112 Base isolated structures
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Sliding System
a) Sliding Base Isolation Systems
It is the second basic type of isolators
This works by limiting the base shear across the
isolator interface
b) Spherical Sliding Base Isolators
The structure is supported by bearing pads that
have curved surface and low friction
During an earthquake the building is free to
slide on the bearings
c) Friction Pendulum Bearing
These are specially designed base isolators
which works on the
principle of simple
pendulum
It increases the natural time
period of oscillation by
causing the structure to
Fig ndash 1113 Elastomeric Isolators Fig ndash 1114 Steel Reinforced Elastomeric
Isolators
Fig ndash 1115 Metallic Roller Bearing
Fig ndash 1116 Spherical Sliding Base
Isolators
Fig ndash 1117 Cross-section of Friction Pendulum Bearing
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slide along the concave inner surface through the frictional interface
It also possesses a re-centering capability
Typically bearings measure 10 m (3 feet) in dia 200 mm (8 inches) in height and weight
being 2000 pounds
d) Advantages of base isolation
Isolate building from ground motion
Building can remain serviceable throughout construction
Lesser seismic loads hence lesser damage to the structure
Minimal repair of superstructure
Does not involve major intrusion upon existing superstructure
e) Disadvantages of base isolation
Expensive
Cannot be applied partially to structures unlike other retrofitting
Challenging to implement in an efficient manner
Allowance for building displacements
Inefficient for high rise buildings
Not suitable for buildings rested on soft soil
112122 Seismic Dampers
Seismic dampers are used in place of structural elements like diagonal braces for controlling
seismic damage in structures
It partly absorbs the seismic energy and reduces the motion of buildings
Types
Viscous Dampers Energy is absorbed by silicon-based fluid passing between piston-
cylinder arrangement
Fig -1118 Cross-section of a Viscous Fluid Damper
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Friction Dampers Energy is absorbed
by surfaces with friction between
rubbing against each other
Yielding Dampers Energy is absorbed
by metallic components that yield
1122 सदसकय सकिर यम सकथमनीय ररटरोफमइ िरीक Member Level or Local Retrofit Methods
The member level retrofit or local retrofit approach is to upgrade the strength of the members
which are seismically deficient This approach is more cost effective as compared to the
structural level retrofit
Jacketing
The most common method of enhancing the individual member strength is jacketing It includes
the addition of concrete steel or fibre reinforced polymer (FRP) jackets for use in confining
reinforced concrete columns beams joints and foundation
Types of jacketing
(1) Concrete jacketing (2) Steel jacketing (3) Strap jacketing
Fig ndash 1119 Friction Dampers
Fig ndash 1120 Yielding Dampers
Fig ndash 1121 Type of Jacketing
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11221 Member level Jacketing
(i) Jacketing of Columns
Different methods of column jacketing are as shown in Figures below
Fig ndash 1122 (b) Column with
CFRP (Carbon Fibre
Reinforced Polymer) Wrap
Fig ndash 1122 (c) Column with Steel Fig ndash 1122 (d) Column with
Jacketing Steel Caging
Fig ndash 1122 (a) Reinforced Concrete Jacketing
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Fig ndash 1122 (e) Construction techniques for Fig ndash 1122 (f) Local strengthening of RC
column jacketing Columns
Fig ndash 1122 (g) Details for provision of longitudinal reinforcement
Fig ndash 1122 (h) Different methods of column jacketing
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(ii) Jacketing of Beam
(iii) Jacketing of Beam-Column Joint
Fig ndash 1123 Different ways of beam jacketing
Fig ndash 1124 Continuity of longitudinal steel in jacketed beams
Fig ndash 1125 Steel cage assembled in the joint
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11222 Table showing the details of reinforced concrete jacketing
Properties of jackets match with the concrete of the existing structure
compressive strength greater than that of the existing
structures by 5 Nmm2 (50 kgcm
2) or at least equal to that
of the existing structure
Minimum width of
jacket 10 cm for concrete cast-in-place and 4 cm for shotcrete
If possible four sided jacket should be used
A monolithic behaviour of the composite column should be
assured
Narrow gap should be provided to prevent any possible
increase in flexural capacity
Minimum area of
longitudinal
reinforcement
3Afy where A is the area of contact in cm2 and fy is in
kgcm2
Spacing should not exceed six times of the width of the new
elements (the jacket in the case) up to the limit of 60 cm
Percentage of steel in the jacket with respect to the jacket
area should be limited between 0015 and 004
At least a 12 mm bar should be used at every corner for a
four sided jacket
Minimum area of
transverse
reinforcement
Designed and spaced as per earthquake design practice
Minimum bar diameter used for ties is not less than 10 mm
diameter anchorage
Due to the difficulty of manufacturing 135 degree hooks on
the field ties made up of multiple pieces can be used
Shear stress in the
interface Provide adequate shear transfer mechanism to assured
monolithic behaviour
A relative movement between both concrete interfaces
(between the jacket and the existing element) should be
prevented
Chipping the concrete cover of the original member and
roughening its surface may improve the bond between the
old and the new concrete
For four sided jacket the ties should be used to confine and
for shear reinforcement to the composite element
For 1 2 3 side jackets as shown in Figures special
reinforcement should be provided to enhance a monolithic
behaviour
Connectors Connectors should be anchored in both the concrete such that
it may develop at least 80 of their yielding stress
Distributed uniformly around the interface avoiding
concentration in specific locations
It is better to use reinforced bars (rebar) anchored with epoxy
resins of grouts as shown in Figure (a)
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11223 Practical aspects in choosing appropriate techniques
Certain issues of practical importance that may help to avoid mistakes in choosing the
appropriate technique are as follows
1) The strengthening of columns by using FRPs or steel jackets is unsuitable for flexible
structures where failure would be controlled by deflection In this case the strengthening
should aim to increase the stiffness
2) It is not favourable to use steel cages or confine with FRPs when an increase in the flexural
capacity of vertical elements is required
3) The application of confinement (with FRPs or steel) to circular or rectangular columns would
increase the ductility and the shear strength and would limit the slippage of overlapping bars
when the lap length has been found to be insufficient However a significant contribution
cannot be expected for columns of rectangular cross section with a large aspect ratio or those
with L-shaped cross sections
4) In the case of columns that have heavily rusted reinforcement strengthening with FRP
jackets (or the application of epoxy glue) will protect the reinforcement from further
oxidation However if the corrosion of the reinforcement is at an advanced stage it is
probable that strengthening may not stop the premature failure of the element
5) The construction of FRP jackets around vertical elements will increase the ductility but it
cannot increase the buckling resistance of the longitudinal reinforcement bars Thus if the
stirrups are too thin in an existing element failure will probably result from the premature
bending of the vertical reinforcement In this case local stress concentrations from the
distressed bars will build up between the stirrups and will lead to a local failure of the jacket
Consequently if bending of the vertical reinforcement has been evaluated as the most likely
cause of column failure the preferable choice for strengthening of the element would be to
place a steel cage
6) In areas where the overlapping of reinforcement bars has been found to be inadequate (short
lap lengths) confining the element with FRPs steel cages or steel jackets will improve the
strength and the ductility of the region considerably However even if it improved the
behaviour it is eventually unfeasible to deter the slipping of bars Consequently when the lap
length of bars has been found to be smaller than 30 of code requirements the solution of
welding of bars must be selected Moreover it must be pointed out that confinement cannot
offer anything to longitudinal bars that are not in the corners of the cross section
7) Experimentally the procedure of placing FRP sheets to strengthen weak beam-column joints
has proved to be particularly effective In practice however this technique has been found to
be difficult to apply due to the presence of slabs and transverse beams The same problems
arise when placing steel plates Other techniques such as the construction of reinforced
concrete jackets or the reconstruction of joints with additional interior reinforcement appear
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to be more beneficial In cases where only a light damage to the joints has been found
repairing with an epoxy resin appears to be particularly effective solution
8) The placing of new concrete in contact with an existing element (by shotcreting and
especially by pouring) will require prior aggravation of the old surface to a depth of at least 6
mm This should be performed by sandblasting or by using suitable mechanical equipment
(for example a scabbler and not just simply a hammer and a chisel) This is to remove the
exterior weak skin of the concrete and to expose the aggregate
9) When placing a new concrete jacket around an existing column it is not always possible to
follow code requirements and place
internal rectangular stirrups to enclose
the middle longitudinal bars as shown
in Fig-1126(a) In this case it is
proposed to place two middle bars in
each side of the jacket so that
octagonal stirrups can be easily
placed as demonstrated in
Fig-1126(b)
In the case where columns have a cross section
with a large aspect ratio the middle longitudinal
bars can be connected by drilling holes through
the section in order to place a S-shaped stirrup as
shown in Fig ndash 1127 After placing stirrups the
remaining void can be filled with epoxy resin In
order to ease placement the S-shaped stirrup can
be prefabricated with one hook and after placing
the second hook can be formed by hand
10) If a thin concrete jacket is to be
placed around a vertical element
and the 135 deg hooks at the ends
of the stirrups are impeded by the
old column it would be
acceptable to decrease the hook
anchorage from 10 times the bar
diameter to 5 or 6 times the bar
diameter as shown in
Fig ndash 1128(a) Otherwise the
ends the stirrups should be
welded together or connected
with special contacts (clamps) as
presented in Fig ndash 1128(b) that have now appeared on the market
(a) (b)
Fig ndash 1126 Placement of internal stirrups in
rectangular cross section
Fig ndash 1127 Placement of an internal
stirrup in a rectangular cross section
with a large aspect ratio
(a) (b)
Fig ndash 1128 Reducing hook lengths and welding the
ends of stirrups
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11) When constructing a jacket around a column it is
important to also strengthen the column joint As shown
in Fig ndash 1129 this can be accomplished by where
possible extending the longitudinal reinforcement bars
around the joint In addition as also shown in
Fig ndash 1129 stirrups must be placed in order to confine
the concrete of the jacket around the joint
In the case where the joint has been found to be
particularly weak a steel diagonal collar can be placed
around the joint before placing the reinforcement as
shown in Fig ndash 1130
12) It is preferable that a new concrete jacket is placed
continuously from the foundation to the top of the building
If this is not possible (due to maintaining the functioning of
the building) it is usual to stop the jacket at the top of the
ground floor level In this case there is a need to anchor the
jacketrsquos longitudinal bars to the existing column This can
be achieved by anchoring a steel plate to the base of the
column of the floor level above and then welding the
longitudinal bars to the anchor plate as shown in Fig ndash
1131
13) In the case where there is a need to reconstruct a heavily damaged column after first shoring
up the column all the defective concrete must be removed so that only good concrete
Fig ndash 1129 Strengthening the
column joint
Fig ndash 1130 Placing a steel diagonal collar
around a weak column joint
Fig ndash 1131 Removal of
defective concrete from a
heavily damaged column
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remains as shown in Fig ndash 1132 Any
buckled reinforcement bars must be welded
to the existing bars Finally the column can
be recast by placing a special non-shrink
concrete
14) In order to anchor new reinforcement bars dowels or anchors with the use of epoxy glue the
diameter of holes drilled into the existing concrete should be roughly 4 mm larger than the
diameter of the bar The best way to remove dust from drilled holes would be to spray water
at the back of the hole The best results (higher adhesive forces) are achieved when the walls
of the hole have been roughened slightly with a small wire brush
15) Care is required when shotcreting in the presence of reinforcement There is a danger of an
accumulation of material building up behind the bars This is usually accredited to material
sticking to the face of bars and may be due to either a low velocity a large firing distance or
insufficient pressure from the compressor
16) The placing of steel plates and especially FRP sheets or fabrics requires special preparation of
the concrete surface to which they will be stuck The rounding of corners and the removal of
surface abnormalities constitute minimal conditions for the application of this technique
17) Two constructional issues that concern the connection of new walls to the old frame require
particular attention The first problem is due to the shrinkage of the new concrete and the
appearance of cracks at the top of the new wall immediately below the old beam in the
region where a good contact between surfaces is essential Here the problem of shrinkage
can be usually dealt with by placing concrete of a particular composition where special
admixtures (for example expansive cements) have been used Alternatively the new wall
could be placed to about 20 cm below the existing beam and after more than 7 days (taking
into account temperature and how new concrete shrinks with time) the void can be filled
with an epoxy or polyster mortar In some cases depending on site conditions (ease of access
dry conditions etc) the new wall can be placed to a height of 2 to 5 mm below the beam and
the void filled with resin glue using the technique of resin injection The second problem
concerns the case of walls from ready-mix concrete and the difficulty of placing the higher
part of the wall due to insufficient access For this reason alone the use of shotcrete should
be the preferred option
Fig ndash 1132 Welding longitudinal bars to an
anchor plate
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113 आरसी भवनो क घ को र समरमनय भकपी कषतियम और उनक उपचमर Common
seismic damage in components of RC Buildings and their remedies
Possible damages in component of RC Buildings which are frequently observed after the
earthquakes are as follows
(i) R C Column
The most common modes of failure of column are as follows
Mode -1 Formation of plastic hinge at the base of ground level columns
Mechanism The column when subjected to seismic
motion its concrete begins to disintegrate and the
load carried by the concrete shifts to longitudinal
reinforcement of the column This additional load
causes buckling of longitudinal reinforcement As a
result the column shortens and looses its ability to
carry even the gravity load
Reasons Insufficient confinement length and
improper confinement in plastic hinge region due to
smaller numbers of ties
Remedies This type of damage is sensitive to the cyclic moments generated during the
earthquake and axial load intensity Consideration is to be paid on plastic hinge length or length
of confinement
Mode ndash 2 Diagonal shear cracking in mid span of columns
Mechanism In older reinforced
concrete building frames column
failures were more frequent since
the strength of beams in such
constructions was kept higher than
that of the columns This shear
failure brings forth loss of axial
load carrying capacity of the
column As the axial capacity
diminishes the gravity loads carried by the column are transferred to neighbouring elements
resulting in massive internal redistribution of forces which is also amplified by dynamic effects
causing spectacular collapse of building
Reason Wide spacing of transverse reinforcement
Remedies To improve understanding of shear strength as well as to understand how the gravity
loads will be supported after a column fails in shear
Fig ndash 1133 Formation of plastic hinge at
the base
Fig ndash 1134 Diagonal shear cracking in mid span of
columns
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Mode ndash 3 Shear and splice failure of longitudinal reinforcement
Mechanism Splices of column
longitudinal reinforcement in
older buildings were
commonly designed for
compression only with
relatively light transverse
reinforcement enclosing the
lap
Under earthquake motion the
longitudinal reinforcement may
be subjected to significant tensile stresses which require lap lengths for tension substantially
exceeding those for compression As a result slip occurs along the splice length with spalling of
concrete
Reasons Deficient lap splices length of column longitudinal reinforcement with lightly spaced
transverse reinforcement particularly if the splices just above the floor slab especially the splices
just above the floor slab which is very common in older construction
Remedies Lap splices should be provided only in the center half of the member length and it
should be proportionate to tension splice Spacing of transverse reinforcement as per IS
139291993
Mode ndash 4 Shear failures in captive columns and short columns
Captive column Column whose deforming ability is restricted and only a fraction of its height
can deform laterally It is due to presence of adjoining non-structural elements columns at
slopping ground partially buried basements etc
Fig - 1135 Shear and splice failure of longitudinal
reinforcement
Fig ndash 1136 Restriction to the Lateral
Displacement of a Column Creating a Captive-
Column Effect
Fig ndash 1137 Captive-column effect in a
building on sloping terrain
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A captive column is full storey slender column whose clear height is reduced by its part-height
contact with a relatively stiff non-structural element such as a masonry infill wall which
constraints its lateral deformation over
the height of contract
The captive column effect is caused by
a non-intended modification to the
original structural configuration of the
column that restricts the ability of the
column to deform laterally by partially
confining it with building components
The column is kept ldquocaptiverdquo by these
components and only a fraction of its
height can deform laterally
corresponding to the ldquofreerdquo portion
thus the term captive column Figure
as given below shows this situation
Short column Column is made shorter than neighbouring column by horizontal structural
elements such as beams girder stair way landing slabs use of grade beams and ramps
Fig ndash 1138 Typical captive-column failure Fig ndash 1139 Column damage due to
captive- column effect
Fig ndash 1140 Captive column caused by ventilation
openings in a partially buried basement
Fig ndash 1141 Short column created by
a stairway landing
Fig ndash 1142 Shear failures in captive columns
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For split-level buildings in order to circumvent the short-column effect the architect should
avoid locating a frame at the vertical plane where the transition between levels occurs For
buildings on slopes special care should be exercised to locate the sloping retaining walls in such
a way that no captive-column effects are induced Where stiff non-structural walls are still
employed these walls should be separated from the structure and in no case can they be
interrupted before reaching the full height of the adjoining columns
Mechanism A reduction in the clear height of captive or short columns increases the lateral
stiffness Therefore these columns are subjected to larger shear force during the earthquake since
the storey shear is distributed in proportion to lateral stiffness of the same floor If these columns
reinforced with conventional longitudinal and transverse reinforcement and subjected to
relatively high axial loading fail by splitting of concrete along their diagonals if the axial
loading level is low the most probable mode of failure is by shear sliding along full depth cracks
at the member ends Moreover in the case of captive column is so effective that usually damage
is shifted to the short non-confined upper section of the column
Reasons Large shear stresses when the structure is subjected to lateral forces are not accounted
for in the standard frame design procedure
Remedies The best solution for captive column or short column is to avoid the situation
otherwise use separation gap in between the non-structural elements and vertical structural
element with appropriate measures against out-of-plane stability of the masonry wall
(ii) R C Beams
The shear-flexure mode of failure is most commonly observed during the earthquakes which is
described as below
Mode ndash 5 Shear-flexure failure
Mechanism Two types of plastic hinges may form in the beams of multi-storied framed
construction depending upon the span of
beams In case of short beams or where
gravity load supported by the beam is
low plastic hinges are formed at the
column ends and damage occurs in the
form of opening of a crack at the end of
beam otherwise there is formation of
plastic hinges at and near end region of
beam in the form of diagonal shear
cracking
Reasons Lack of longitudinal compressive reinforcement infrequent transverse reinforcement in
plastic hinge zone bad anchorage of the bottom reinforcement in to the support or dip of the
longitudinal beam reinforcement bottom steel termination at face of column
Fig ndash 1143 Shear-flexure failure
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Remedies Adequate flexural and shear strength must be provided and verification by design
calculation is essential The beams should not be too stiff with respect to adjacent columns so
that the plastic hinging will occur in beam rather than in column To ensure that the plastic hinges
zones in beams have adequate ductility the following considerations must be considered
Lower and upper limits on the amount of longitudinal flexural tension steel
A limit on the ration of the steel on one side of the beam to that of on the other side
Minimum requirements for the spacing and size of stirrups to restrain buckling of the
longitudinal reinforcement
(iii) R C Beam-Column Joints
The most common modes of failure in beam-column joint are as follows
Mode ndash 6 shear failure in beam-column joint
Mechanism The most common
failure observed in exterior joints are
due to either high shear or bond
(anchorage) under severe
earthquakes Plastic hinges are
formed in the beams at the column
faces As a result cracks develop
throughout the overall beam depth
Bond deterioration near the face of
the column causes propagation of
beam reinforcement yielding in the joint and a shortening of the bar length available for force
transfer by bond causing horizontal bar slippage in the joint In the interior joint the beam
reinforcement at both the column faces undergoes different stress conditions (compression and
tension) because of opposite sights of seismic bending moments results in failure of joint core
Reasons Inadequate anchorage of flexural steel in beams lack of transverse reinforcement
Remedies Exterior Joint ndash The provision on anchorage stub for the beam reinforcement
improves the performance of external joints by preventing spalling of concrete cover on the
outside face resulting in loss of flexural strength of the column This increases diagonal strut
action as well as reduces steel congestion as the beam bars can be anchored clear of the column
bars
(iv) R C Slab
Generally slab on beams performed well during earthquakes and are not dangerous but cracks in
slab creates serious aesthetic and functional problems It reduces the available strength stiffness
and energy dissipation capacity of building for future earthquake In flat slab construction
punching shear is the primary cause of failure The common modes of failure are
Fig - 1144 Shear failure in beam-column joint
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Mode ndash 7 Shear cracking in slabs
Mechanism Damage to slab oftenly
occurs due to irregularities such as large
openings at concentration of earthquake
forces close to widely spaced shear
walls at the staircase flight landings
Reasons Existing micro cracks which
widen due to shaking differential
settlement
Remedies
Use secondary reinforcement in the bottom of the slab
Avoid the use of flat slab in high seismic zones provided this is done in conjunction with a
stiff lateral load resisting system
(v) R C Shear Walls
Shear walls generally performed well during the earthquakes Four types of failure modes are
generally observed
Mode ndash 8 Four types of failure modes are generally observed
(i) Diagonal tension-compression failure in the form of cross-shaped shear cracking
(ii) Sliding shear failure cracking at interface of new and old concrete
(iii) Flexure and compression in bottom end region of wall and finally
(iv) Diagonal tension in the form of X shaped cracking in coupling beams
Fig ndash 1145 Shear cracking in slabs
Fig ndash 1146 Diagonal tension-compression Sliding shear Flexure and compression
failure
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Mechanism Shear walls are subjected to shear and flexural deformation depending upon the
slenderness ratio Therefore the damage in shear walls may generally occurs due to inadequate
shear and flexure capacity of wall Slender walls are governed by their flexural strength and
cracking occurs in the form of yielding of main flexure reinforcement in the plastic hinge region
normally at the base of the wall Squat walls are governed by their shear strength and failure
takes place due to diagonal tension or diagonal compression in the form of inclined cracking
Coupling beams between shear walls or piers may also damage due to inadequate shear and
flexure capacity Sometimes damage occurs at the construction joints in the form of slippage and
related drift
Reasons
Flexuralboundary compression failure Inadequate transverse confining reinforcement to the
main flexural reinforcement near the outer edge of wall in boundary elements
Flexurediagonal tension Inadequate horizontal shear reinforcement
Sliding shear Absence of diagonal reinforcement across the potential sliding planes of the
plastic hinge zone
Coupling beams Inadequate stirrup reinforcement and no diagonal reinforcement
Construction joint Improper bonding between two surfaces
Remedies
The concrete shear walls must have boundary elements or columns thicker than walls which
will carry the vertical load after shear failure of wall
A proper connection between wall versus diaphragm as well as wall versus foundation to
complete the load path
Proper bonding at construction joint in the form of shear friction reinforcement
Provision of diagonal steel in the coupling beam
Fig ndash 1147 Diagonal tension in the form of X shaped
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(v) Infill Walls
Infill panels in reinforced concrete frames are the cause of unequal distribution of lateral forces
in the different frames of a building producing vertical and horizontal irregularities etc the
common mode of failure of infill masonry are in plane or shear failure
Mode ndash 9 Shear failure of masonry infill
Mechanism Frame with infill possesses much more lateral stiffness than the bare frame and
hence initially attracts most of the lateral force during an earthquake Being brittle the infill
starts to disintegrate as soon as its strength is reached Infills that were not adequately tied to the
surrounding frames sometimes dislodges by out-of-plane seismic excitations
Reasons Infill causes asymmetry of load application resulting in increased torsional forces and
changes in the distribution of shear forces between lateral load resisting system
Remedies Two strategies are possible either complete separation between infill walls and frame
by providing separation joint so that the two systems do not interact or complete anchoring
between frame and infill to act as an integral unit Horizontal and vertical reinforcement may also
be used to improve the strength stiffness and deformability of masonry infill walls
(vi) Parapets
Un-reinforced concrete parapets with large height-to-thickness ratio and not in proper anchoring
to the roof diaphragm may also constitute a hazard The hazard posed by a parapet increases in
direct proportion to its height above building base which has been generally observed
The common mode of failure of parapet wall is against out-of-plane forces which is described as
follows
Mode ndash 10 Brittle flexure out-of-plane failure
Mechanism Parapet walls are acceleration sensitive in the out-of-plane direction the result is
that they may become disengaged and topple
Fig ndash 1148 Shear failure of masonry infill
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Reasons Not properly braced
Remedies Analysed for acceleration forces and braced and connected with roof diaphragm
114 चचनमई सरचनमओ की रटरोफिट ग Retrofitting of Masonry Structures
(a) Principle of Seismic Safety of Masonry Buildings
Integral box action
Integrity of various components
- Roof to wall
- Wall to wall at corners
- Wall to foundation
Limit on openings
(b) Methods for Retrofitting of Masonry Buildings
Repairing (Improving existing masonry strength)
Stitching of cracks
Grouting with cement or epoxy
Use of CFRP (Carbon Fibre Reinforced Polymer) strips
Fig ndash 1149 Brittle flexure out-of-plane failure
(a) (b)
Fig ndash 1150 (a) Stitching of cracks Fig ndash 1150 (b) Repair of damaged member in
masonry walls
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(c) Retrofitting of Earthquake vulnerable buildings
External binding or jacketing
Shotcreting
Strengthening of wall intersections
Strengthening by cross wall
Strengthening by buttresses
Strengthening of arches
Fig ndash 1151 Integral Box action
(a) (b)
Fig - 1152 (a) Strengthening of Wall Fig - 1152 (b) Strengthening by
intersections cross wall
(a) (b)
Fig ndash 1153 (a) Strengthening by Fig ndash 1153 (b) Strengthening of Arches
Buttresses
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पररलिष Annexure ndash I
भारिीय भको पी सोतििाएा Indian Seismic Codes
Development of building codes in India started rather early Today India has a fairly good range
of seismic codes covering a variety of structures ranging from mud or low strength masonry
houses to modern buildings However the key to ensuring earthquake safety lies in having a
robust mechanism that enforces and implements these design code provisions in actual
constructions
भको पी तिजाइन कोि का मितव Importance of Seismic Design Codes
Ground vibrations during earthquakes cause forces and deformations in structures Structures
need to be designed to withstand such forces and deformations Seismic codes help to improve
the behaviour of structures so that they may withstand the earthquake effects without significant
loss of life and property An earthquake-resistant building has four virtues in it namely
(a) Good Structural Configuration Its size shape and structural system carrying loads are such
that they ensure a direct and smooth flow of inertia forces to the ground
(b) Lateral Strength The maximum lateral (horizontal) force that it can resist is such that the
damage induced in it does not result in collapse
(c) Adequate Stiffness Its lateral load resisting system is such that the earthquake-induced
deformations in it do not damage its contents under low-to moderate shaking
(d) Good Ductility Its capacity to undergo large deformations under severe earthquake shaking
even after yielding is improved by favourable design and detailing strategies
Seismic codes cover all these aspects
भारिीय भको पी सोतििाएा Indian Seismic Codes
Seismic codes are unique to a particular region or country They take into account the local
seismology accepted level of seismic risk building typologies and materials and methods used
in construction The first formal seismic code in India namely IS 1893 was published in 1962
Today the Bureau of Indian Standards (BIS) has the following seismic codes
1 IS 1893 (Part I) 2002 Indian Standard Criteria for Earthquake Resistant Design of
Structures (5 Revision)
2 IS 4326 1993 Indian Standard Code of Practice for Earthquake Resistant Design and
Construction of Buildings (2nd Revision)
3 IS 13827 1993 Indian Standard Guidelines for Improving Earthquake Resistance of
Earthen Buildings
4 IS 13828 1993 Indian Standard Guidelines for Improving Earthquake Resistance of Low
Strength Masonry Buildings
5 IS 13920 1993 Indian Standard Code of Practice for Ductile Detailing of Reinforced
Concrete Structures Subjected to Seismic Forces
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6 IS 13935 1993 Indian Standard Guidelines for Repair and Seismic Strengthening of
Buildings
The regulations in these standards do not ensure that structures suffer no damage during
earthquake of all magnitudes But to the extent possible they ensure that structures are able to
respond to earthquake shakings of moderate intensities without structural damage and of heavy
intensities without total collapse
IS 1893 (Part I) 2002
IS 1893 is the main code that provides the seismic zone map and specifies seismic design force
This force depends on the mass and seismic coefficient of the structure the latter in turn
depends on properties like seismic zone in which structure lies importance of the structure its
stiffness the soil on which it rests and its ductility For example a building in Bhuj will have
225 times the seismic design force of an identical building in Bombay Similarly the seismic
coefficient for a single-storey building may have 25 times that of a 15-storey building
The revised 2002 edition Part 1 of IS1893 contains provisions that are general in nature and
those applicable for buildings The other four parts of IS 1893 will cover
a) Liquid-Retaining Tanks both elevated and ground supported (Part 2)
b) Bridges and Retaining Walls (Part 3)
c) Industrial Structures including Stack Like Structures (Part 4) and
d) Dams and Embankments (Part 5)
These four documents are under preparation In contrast the 1984 edition of IS1893 had
provisions for all the above structures in a single document
Provisions for Bridges
Seismic design of bridges in India is covered in three codes namely IS 1893 (1984) from the
BIS IRC 6 (2000) from the Indian Roads Congress and Bridge Rules (1964) from the Ministry
of Railways All highway bridges are required to comply with IRC 6 and all railway bridges
with Bridge Rules These three codes are conceptually the same even though there are some
differences in their implementation After the 2001 Bhuj earthquake in 2002 the IRC released
interim provisions that make significant improvements to the IRC6 (2000) seismic provisions
IS 4326 1993 (Reaffirmed 2003)
This code covers general principles for earthquake resistant buildings Selection of materials
and special features of design and construction are dealt with for the following types of
buildings timber constructions masonry constructions using rectangular masonry units and
buildings with prefabricated reinforced concrete roofingflooring elements The code
incorporates Amendment No 3 (January 2005)
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IS 13827 1993 and IS 13828 1993
Guidelines in IS 13827 deal with empirical design and construction aspects for improving
earthquake resistance of earthen houses and those in IS 13828 with general principles of
design and special construction features for improving earthquake resistance of buildings of
low-strength masonry This Masonry includes burnt clay brick or stone masonry in weak
mortars like clay-mud These standards are applicable in seismic zones III IV and V
Constructions based on them are termed non-engineered and are not totally free from collapse
under seismic shaking intensities VIII (MMI) and higher Inclusion of features mentioned in
these guidelines may only enhance the seismic resistance and reduce chances of collapse
IS 13920 1993 (Reaffirmed 2003)
In India reinforced concrete structures are designed and detailed as per the Indian Code IS 456
(2002) However structures located in high seismic regions require ductile design and
detailing Provisions for the ductile detailing of monolithic reinforced concrete frame and shear
wall structures are specified in IS 13920 (1993) After the 2001 Bhuj earthquake this code has
been made mandatory for all structures in zones III IV and V Similar provisions for seismic
design and ductile detailing of steel structures are not yet available in the Indian codes
IS 13935 1993
These guidelines cover general principles of seismic strengthening selection of materials and
techniques for repairseismic strengthening of masonry and wooden buildings The code
provides a brief coverage for individual reinforced concrete members in such buildings but
does not cover reinforced concrete frame or shear wall buildings as a whole Some guidelines
are also laid down for non-structural and architectural components of buildings
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पररलिष Annexure ndash II
Checklist Multiple Choice Questions for Points to be kept in mind during
Construction of Earthquake Resistant Building
S No Description Observer Remarks
1 Seismic Zone in which building is located
i) Zone II ndash Least Seismically Prone Region
ii) Zone III ndash
iii) Zone IV ndash
iv) Zone V ndash Most Seismically Prone Region
Choose Zone
2 Environment condition to which building is exposed
a) Mild b) Moderate c) Severe d) Very Severe e) Extreme
Choose Condition
3 Whether the building is located in Flood Zone YesNo
4 Whether the building is located in Land Slide Zone ie building is on
hill slope or Plane Area
YesNo
5 Type of soil at founding level
a) Rock or Hard Soil
b) Medium Soil
c) Soft Soil
Choose type of soil
6 Type of Building
I) Load Bearing Masonry Building
a) Brick Masonry Construction
b) Stone Masonry construction
II) RCC Framed Structure
a) Regular frame
b) Regular Frame with shear wall
c) Irregular Frame
d) Irregular Frame with shear wall
e) Soft Story Building
Choose type of
building
7 No of Story above Ground Level with provision of Future Extension Mention Storey
8 Category of Building considering Seismic Zone and Importance
Factor (As per Table ndash 102)
i) Category B ndash Building in Seismic Zone II with Importance Factor
10
ii) Category E- Building in Seismic Zone II with Importance Factor
10 and 150
Choose category
9 Bricks should not have compressive strength less than 350 MPa YesNo
10 Minimum wall thickness of brick masonry
i) 1 Brick ndash Single Storey Construction
ii) 1 frac12 Brick ndash In bottom storey up to 3 storey construction amp
1 Brick in top storey with brick masonry
Choose appropriate
11 Height of building is restricted to
i) For A B amp C categories ndash G+2 with flat roof G+1 plus anti for
pitched roof when height of each story not exceed 3 m
ii) D category ndash G+1 with flat Roof
- Ground plus attic for pitched roof
Choose appropriate
12 Max Height of Brick masonry Building ndash 15 m (max 4 storey) YesNo
13 Mortar mix shall be as per Table ndash 102 for category A to E Choose Mortar
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14 Height of Stone Masonry wall
i) For Categories AampB ndash
a) When built in Lime-Sand or Mud mortar
ndash Two storey with flat roof or One Storey plus attic
b) When build in cement sand 16 mortar
- One story higher
ii) For Categories CampD ndash
a) When built in cement Sand 16 Mortar
- Two storey with flat roof or One Storey plus attic for pitched
roof
b) When build in lime sand or Mud mortar
- One story with flat roof or One Story plus attic
Choose appropriate
15 Through stone at full length equal to wall thickness in every 600 mm
lift at not more than 120 m apart horizontally has been provided
YesNo
16 Through stone and Bond Element as per Fig 1024 has been provided YesNo
17 Horizontal Bands
a) Plinth Band
b) Lintel Band
c) Roof Bond
d) Gable Bond
For Over Strengthening Arrangement for Category D amp E Building
have been provided
YesNo
18 Bond shall be made up of Reinforced Concrete of Grade not leaner
than M15 or Reinforced brick work in cement mortar not leaner than
13
YesNo
19 Bond shall be of full width of wall not less than 75 mm in depth and
reinforced with steel as shown in Table ndash 106
YesNo
20 Vertical steel at corners amp junction of wall which are up to 340 mm
(1 frac12 brick) thick shall be provided as shown in Table ndash 101
YesNo
21 General principal for planning building are
i) Building should be as light as possible
ii) All parts of building should be tied together to act as one unit
iii) Projecting part should be avoided
iv) Building having plans with shape L T E and Y shall preferably
be separated in to rectangular parts
v) Structure not to be founded on loose soil which will subside or
liquefy during Earthquake resulting in large differential
settlement
vi) Heavy roofing material should be avoided
vii) Large stair hall shall be separated from Rest of the Building by
means of separation or crumple section
viii) All of the above
ix) None of the above
Choose Correct
22 Structural irregularities may be
i) Horizontal Irregularities
ii) Vertical Irregularities
iii) All of the above
iv) None of the above
Choose Correct
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23 Horizontal Irregularities are
i) Asymmetrical plan shape (eg LTUF)
ii) Horizontal resisting elements (diaphragms)
iii) All of the above
iv) None of the above
Choose Correct
24 Horizontal Irregularities result in
i) Torsion
ii) Diaphragm deformation
iii) Stress Concentration
iv) All of the above
v) None of the above
Choose Correct
25 Vertical Irregularities are
i) Sudden change of stiffness over height of building
ii) Sudden change of strength over height of building
iii) Sudden change of geometry over height of building
iv) Sudden change of mass over height of building
v) All of the above
vi) None of the above
Choose Correct
26 Soft story in one
i) Which has lateral stiffness lt 70 of story above
ii) Which has lateral stiffness lt 80 of average lateral stiffness of 3
storeys above
iii)All of the above
vi) None of the above
Choose Correct
27 Extreme soft storey in one
i) Which has lateral stiffness lt 60 of storey above
ii) Which has lateral stiffness lt 70 of average lateral stiffness of 3
storeys above
iii)All of the above
iv)None of the above
Choose Correct
28 Weak Storey is one
i) Which has lateral strength lt 80 of storey above
ii) Which has lateral strength lt 80 of storey above
iii)All of the above
iv)None of the above
Choose Correct
29 Natural Period of Building
It is the time taken by the building to undergo one complete
cycle of oscillation during shaking
True False
30 Fundamental Natural Period of Building
Natural period with smallest Natural Frequency ie with largest
natural period is called Fundamental Natural Period
True False
31
Type of building frame system
i) Ordinary RC Moment Resisting Frame (OMRF)
ii) Special RC Moment Resisting Frame (SMRF)
iii) Ordinary Shear Wall with OMRF
iv) Ordinary Shear Wall with SMRF
v) Ductile Shear wall with OMRF
vi) Ductile Shear wall with SMRF
vii) All of the above
Choose Correct
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32 Zone factor to be considered for
i) Zone II ndash 010
ii) Zone III ndash 016
iii) Zone IV ndash 024
iv) Zone V ndash 036
True False
33 Importance Factor
i) Important building like school hospital railway station 15
ii) All other buildings 10
True False
34 Design of Earthquake effect is termed as
i) Earthquake Proof Design
or
ii) Earthquake Resistant Design
Choose Correct
35 Seismic Analysis is carried out by
i) Dynamic analysis procedure [Clause 78 of IS1893 (Part I) 2002]
ii) Simplified method referred as Lateral Force Procedure [Clause
75 of IS 1893 (Part I) 2002]
True False
36 Dynamic Analysis is performed for following buildings
(a) Regular Building gt 40 m height in Zone IV amp V
gt 90 height in Zone II amp III
(b) Irregular Building
gt 12 m all framed building in Zone IV amp V
gt 40 m all framed building in Zone II and III
True False
37 Base Shear for Lateral Force Procedure is
VB = Ah W =
True False
38 Distribution of Base Shear to different Floor level is
True False
39 Concept of capacity design is to
Ensure that brittle element will remain elastic at all loads prior to
failure of ductile element
True False
40 lsquoStrong Column ndash Weak Beamrsquo Philosophy is
For a building to remain safe during Earthquake shacking columns
should be stronger than beams and foundation should be stronger
than columns
True False
41 Rigid Diaphragm Action is
Geometric distortion of Slab in horizontal plane under influence of
horizontal Earthquake force is negligible This behaviour is known
as Rigid Diaphragm Action
True False
42 Soft storied buildings are
Column on Ground Storey do not have infill walls (of either
masonry or RC)
True False
43 Soft Storey or Open Ground Story is also termed as weak storey True False
44 Short columns in building suffer significant damage during an earth-
quake
True False
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45 Building can be protected from damage due to Earthquake effect by
using
a) Base Isolation Devices
b) Seismic Dampers
True False
46 Idea behind Base Isolation is
To detach building from Ground so that EQ motion are not
transmitted through the building or at least greatly reduced
True False
47 Base Isolation is done through
Flexible Pads connected to building and foundation True False
48 Seismic Dampers are
(i) Special devices to absorb the energy provided by Ground Motion
to the building
(ii) They act like hydraulic shock absorber in cars
True False
49 Commonly used Seismic Dampers are
(i) Viscous Dampers
(ii) Friction Dampers
(iii) Yielding Dampers
True False
50 For Ductility Requirement
(i) Min Grade of Concrete shall be M20 for all buildings having
more than 3 storeys in height
(ii) Steel Reinforcement of Grade Fe 415 or less only shall be used
(iii) Grade Fe 500 amp Fe 550 having elongation more than 145 may
be used
True False
51 For Ductility Requirement Flexure Members shall satisfy the
following requirement
(i) width of member shall not be less than 200 mm
(ii) width to depth ratio gt 03
(iii) depth of member D lt 14th of clear span
(iv) Factored Axial Stress on the member under Earthquake loading
shall not be greater than 01 fck
True False
52 For Ductility Requirement Longitudinal reinforcement in Flexure
Member shall satisfy the following requirements
i) Top and bottom reinforcement consist of at least 2 bars
throughout member length
ii) Tensile Steel Ratio on any face at any section shall not be less
than ρmin = (024 radic fck) fy
iii) Max Steel ratio on any face at any section shall not exceed
ρmax = 0025
iv) + ve steel at Joint face must be at least equal to half the ndashve steel
at that face
v) Steel provided at each of the top amp bottom face of the member
at any section along its length shall be at least equal to 14th of
max ndashve moment steel provided at the face of either joint
True False
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(vi) Detailing of Reinforcement at Beam-Column Joint
(vii) Detailing of Splicing
53 For Ductile Requirement in compression member
i) Minimum diversion of member shall not be less than 200 mm
ii) In Frames with beams cc Span gt 5m or
unsupported length of column gt 4 m shortest dimension shall not
be less than 300 mm
iii) Ratio of shortest cross sectional dimension to the perpendicular
dimension shall probably not less than 04
True False
54 For Ductile Requirement Longitudinal reinforcement in compression
member shall satisfy the following requirements
i) Lap splice shall be provided only in the central half of the member
length proportional as tension splice
ii) Hoop shall be provided over entire splice length at spacing not
greater than 150 mm
iii) Not more than 50 bar shall be spliced at one section
True False
55 When a column terminates into a footing or mat special confining
reinforcement shall extend at least 300 mm into the footing or mat
True False
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सोदभयगरोथ सची BIBLIOGRAPHY
1 Guidelines for Earthquake Resistant Non-Engineered Construction reprinted by
Indian Institute of Technology Kanpur 208016 India (Source wwwniceeorg)
2 IS 1893 (Part 1) 2002 Criteria for Earthquake Resistant Design Of Structures
PART- 1 GENERAL PROVISIONS AND BUILDINGS (Fifth Revision )
3
IS 4326 1993 (Reaffirmed 1998) Edition 32 (2002-04) Earthquake Resistant
Design and Construction of Buildings ndash Code of Practice ( Second Revision )
(Incorporating Amendment Nos 1 amp 2)
4 IS 13828 1993 (Reaffirmed 1998) Improving Earthquake Resistance of Low
Strength Masonry Buildings ndash Guidelines
5
IS 13920 1993 (Reaffirmed 1998) Edition 12 (2002-03) Ductile Detailing of
Reinforced Concrete Structures subjected to Seismic Forces ndash Code of Practice
(Incorporating Amendment Nos 1 amp 2)
6 IS 13935 1993 (Reaffirmed 1998) Edition 11 (2002-04) Repair and Seismic
Strengthening of Buildings ndash Guidelines (Incorporating Amendment No 1)
7
Earthquake Tips authored by Prof C V R Murty IIT Kanpur and sponsored by
Building Materials and Technology Promotion Council New Delhi India
(Source www wwwiitkacin)
8
Earthquake Engineering Practice Volume 1 Issue 1 March 2007 published by
National Information Center of Earthquake Engineering IIT Kanpur Kanpur
208016
9 Earthquake Resistant Design of Structures by Pankaj Agarwal and Manish
Shrikhande published by PHI Learning Private Limited Delhi 110092 (2015)
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तटपपणी NOTES
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तटपपणी NOTES
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हमारा उददशय
अनरकषि परौधौधगकी और कायापरिाली को उननयन करना तथा उतपादकता और
रलव की पररसमपवियो एव िनशजतत क ननषपादन म सधार करना जिसस
अतववाियो म ववशवसनीयता उपयोधगता और दकषता परापत की िा सकA
Our Objective
To upgrade Maintenance Technologies and Methodologies and achieve
improvement in productivity and performance of all Railway assets and
manpower which inter-alia would cover Reliability Availability and
Utilisation
तिसलमर Disclaimer
The document prepared by CAMTECH is meant for the dissemination of the knowledge information
mentioned herein to the field staff of Indian Railways The contents of this handbookbooklet are only for
guidance Most of the data amp information contained herein in the form of numerical values are indicative
and based on codes and teststrials conducted by various agencies generally believed to be reliable While
reasonable care and effort has been taken to ensure that information given is at the time believed to be fare
and correct and opinion based thereupon are reasonable Due to very nature of research it can not be
represented that it is accurate or complete and it should not be relied upon as such The readeruser is
supposed to refer the relevant codes manuals available on the subject before actual implementation in the
field
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Hkkjrh jsy jkrdquoV ordf dh thou js[kk ---hellip
INDIAN RAILWAYS Lifeline to the nation hellip
If you have any suggestion amp comments please write to us
Contact person Joint Director (Civil)
Phone (0751) - 2470869
Fax (0751) ndash 2470841
Email dircivilcamtechgmailcom
Charbagh Railway Station Lucknow